diff --git a/python/plugins/processing/algs/qgis/BoundingBox.py b/python/plugins/processing/algs/qgis/BoundingBox.py
index 22a050fe34a..5cd7b693635 100644
--- a/python/plugins/processing/algs/qgis/BoundingBox.py
+++ b/python/plugins/processing/algs/qgis/BoundingBox.py
@@ -66,7 +66,7 @@ class BoundingBox(GeoAlgorithm):
         layer = QgsProcessingUtils.mapLayerFromString(self.getParameterValue(self.INPUT_LAYER), context)
 
         writer = self.getOutputFromName(
-            self.OUTPUT_LAYER).getVectorWriter(layer.fields().toList(), QgsWkbTypes.Polygon, layer.crs(), context)
+            self.OUTPUT_LAYER).getVectorWriter(layer.fields(), QgsWkbTypes.Polygon, layer.crs(), context)
 
         features = QgsProcessingUtils.getFeatures(layer, context)
         total = 100.0 / QgsProcessingUtils.featureCount(layer, context)
diff --git a/python/plugins/processing/algs/qgis/CheckValidity.py b/python/plugins/processing/algs/qgis/CheckValidity.py
index 442adbbbcf2..d2168d8de13 100644
--- a/python/plugins/processing/algs/qgis/CheckValidity.py
+++ b/python/plugins/processing/algs/qgis/CheckValidity.py
@@ -30,7 +30,13 @@ import os
 from qgis.PyQt.QtGui import QIcon
 from qgis.PyQt.QtCore import QVariant
 
-from qgis.core import QgsSettings, QgsGeometry, QgsFeature, QgsField, QgsWkbTypes, QgsProcessingUtils
+from qgis.core import (QgsSettings,
+                       QgsGeometry,
+                       QgsFeature,
+                       QgsField,
+                       QgsWkbTypes,
+                       QgsProcessingUtils,
+                       QgsFields)
 from processing.core.GeoAlgorithm import GeoAlgorithm
 from processing.core.parameters import ParameterVector
 from processing.core.parameters import ParameterSelection
@@ -110,18 +116,16 @@ class CheckValidity(GeoAlgorithm):
         valid_count = 0
 
         invalid_output = self.getOutputFromName(self.INVALID_OUTPUT)
-        invalid_fields = layer.fields().toList() + [
-            QgsField(name='_errors',
-                     type=QVariant.String,
-                     len=255)]
+        invalid_fields = layer.fields()
+        invalid_fields.append(QgsField('_errors',
+                                       QVariant.String,
+                                       255))
         invalid_writer = invalid_output.getVectorWriter(invalid_fields, layer.wkbType(), layer.crs(), context)
         invalid_count = 0
 
         error_output = self.getOutputFromName(self.ERROR_OUTPUT)
-        error_fields = [
-            QgsField(name='message',
-                     type=QVariant.String,
-                     len=255)]
+        error_fields = QgsFields()
+        error_fields.append(QgsField('message', QVariant.String, 255))
         error_writer = error_output.getVectorWriter(error_fields, QgsWkbTypes.Point, layer.crs(), context)
         error_count = 0
 
diff --git a/python/plugins/processing/algs/qgis/ConcaveHull.py b/python/plugins/processing/algs/qgis/ConcaveHull.py
index e44d4dde184..eae338c5230 100644
--- a/python/plugins/processing/algs/qgis/ConcaveHull.py
+++ b/python/plugins/processing/algs/qgis/ConcaveHull.py
@@ -136,7 +136,7 @@ class ConcaveHull(GeoAlgorithm):
         feedback.setProgressText(self.tr('Saving data...'))
         feat = QgsFeature()
         QgsProcessingUtils.getFeatures(dissolved_layer, context).nextFeature(feat)
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields().toList(), QgsWkbTypes.Polygon,
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields(), QgsWkbTypes.Polygon,
                                                                      layer.crs(), context)
         geom = feat.geometry()
         if no_multigeom and geom.isMultipart():
diff --git a/python/plugins/processing/algs/qgis/ConvexHull.py b/python/plugins/processing/algs/qgis/ConvexHull.py
index fbe9293bdb2..3ef3090d6bc 100644
--- a/python/plugins/processing/algs/qgis/ConvexHull.py
+++ b/python/plugins/processing/algs/qgis/ConvexHull.py
@@ -31,7 +31,12 @@ import os
 from qgis.PyQt.QtGui import QIcon
 from qgis.PyQt.QtCore import QVariant
 
-from qgis.core import QgsField, QgsFeature, QgsGeometry, QgsWkbTypes, QgsProcessingUtils
+from qgis.core import (QgsField,
+                       QgsFeature,
+                       QgsGeometry,
+                       QgsWkbTypes,
+                       QgsProcessingUtils,
+                       QgsFields)
 
 from processing.core.GeoAlgorithm import GeoAlgorithm
 from processing.core.GeoAlgorithmExecutionException import GeoAlgorithmExecutionException
@@ -96,11 +101,11 @@ class ConvexHull(GeoAlgorithm):
                 f.setType(QVariant.String)
                 f.setLength(255)
 
-        fields = [QgsField('id', QVariant.Int, '', 20),
-                  f,
-                  QgsField('area', QVariant.Double, '', 20, 6),
-                  QgsField('perim', QVariant.Double, '', 20, 6)
-                  ]
+        fields = QgsFields()
+        fields.append(QgsField('id', QVariant.Int, '', 20))
+        fields.append(f)
+        fields.append(QgsField('area', QVariant.Double, '', 20, 6))
+        fields.append(QgsField('perim', QVariant.Double, '', 20, 6))
 
         writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fields, QgsWkbTypes.Polygon, layer.crs(), context)
 
diff --git a/python/plugins/processing/algs/qgis/Delaunay.py b/python/plugins/processing/algs/qgis/Delaunay.py
index bb7c7e4fb3a..54c6e1c043e 100644
--- a/python/plugins/processing/algs/qgis/Delaunay.py
+++ b/python/plugins/processing/algs/qgis/Delaunay.py
@@ -31,7 +31,14 @@ import os
 from qgis.PyQt.QtGui import QIcon
 from qgis.PyQt.QtCore import QVariant
 
-from qgis.core import QgsField, QgsFeatureRequest, QgsFeature, QgsGeometry, QgsPoint, QgsWkbTypes, QgsProcessingUtils
+from qgis.core import (QgsField,
+                       QgsFeatureRequest,
+                       QgsFeature,
+                       QgsGeometry,
+                       QgsPoint,
+                       QgsWkbTypes,
+                       QgsProcessingUtils,
+                       QgsFields)
 
 from processing.core.GeoAlgorithm import GeoAlgorithm
 from processing.core.GeoAlgorithmExecutionException import GeoAlgorithmExecutionException
@@ -72,9 +79,10 @@ class Delaunay(GeoAlgorithm):
     def processAlgorithm(self, context, feedback):
         layer = QgsProcessingUtils.mapLayerFromString(self.getParameterValue(self.INPUT), context)
 
-        fields = [QgsField('POINTA', QVariant.Double, '', 24, 15),
-                  QgsField('POINTB', QVariant.Double, '', 24, 15),
-                  QgsField('POINTC', QVariant.Double, '', 24, 15)]
+        fields = QgsFields()
+        fields.append(QgsField('POINTA', QVariant.Double, '', 24, 15))
+        fields.append(QgsField('POINTB', QVariant.Double, '', 24, 15))
+        fields.append(QgsField('POINTC', QVariant.Double, '', 24, 15))
 
         writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fields, QgsWkbTypes.Polygon, layer.crs(), context)
 
diff --git a/python/plugins/processing/algs/qgis/DensifyGeometries.py b/python/plugins/processing/algs/qgis/DensifyGeometries.py
index 1f59ef6999c..c35e78eda10 100644
--- a/python/plugins/processing/algs/qgis/DensifyGeometries.py
+++ b/python/plugins/processing/algs/qgis/DensifyGeometries.py
@@ -82,7 +82,7 @@ class DensifyGeometries(GeoAlgorithm):
         isPolygon = layer.geometryType() == QgsWkbTypes.PolygonGeometry
 
         writer = self.getOutputFromName(
-            self.OUTPUT).getVectorWriter(layer.fields().toList(), layer.wkbType(), layer.crs(), context)
+            self.OUTPUT).getVectorWriter(layer.fields(), layer.wkbType(), layer.crs(), context)
 
         features = QgsProcessingUtils.getFeatures(layer, context)
         total = 100.0 / QgsProcessingUtils.featureCount(layer, context)
diff --git a/python/plugins/processing/algs/qgis/DensifyGeometriesInterval.py b/python/plugins/processing/algs/qgis/DensifyGeometriesInterval.py
index e99e5b2a343..fff1d5a7169 100644
--- a/python/plugins/processing/algs/qgis/DensifyGeometriesInterval.py
+++ b/python/plugins/processing/algs/qgis/DensifyGeometriesInterval.py
@@ -77,7 +77,7 @@ class DensifyGeometriesInterval(GeoAlgorithm):
         isPolygon = layer.geometryType() == QgsWkbTypes.PolygonGeometry
 
         writer = self.getOutputFromName(
-            self.OUTPUT).getVectorWriter(layer.fields().toList(), layer.wkbType(), layer.crs(), context)
+            self.OUTPUT).getVectorWriter(layer.fields(), layer.wkbType(), layer.crs(), context)
 
         features = QgsProcessingUtils.getFeatures(layer, context)
         total = 100.0 / QgsProcessingUtils.featureCount(layer, context)
diff --git a/python/plugins/processing/algs/qgis/Dissolve.py b/python/plugins/processing/algs/qgis/Dissolve.py
index 36b3722a035..8a6173c649c 100644
--- a/python/plugins/processing/algs/qgis/Dissolve.py
+++ b/python/plugins/processing/algs/qgis/Dissolve.py
@@ -81,7 +81,7 @@ class Dissolve(GeoAlgorithm):
         vlayerA = QgsProcessingUtils.mapLayerFromString(self.getParameterValue(Dissolve.INPUT), context)
 
         writer = self.getOutputFromName(
-            Dissolve.OUTPUT).getVectorWriter(vlayerA.fields().toList(), vlayerA.wkbType(), vlayerA.crs(), context)
+            Dissolve.OUTPUT).getVectorWriter(vlayerA.fields(), vlayerA.wkbType(), vlayerA.crs(), context)
 
         outFeat = QgsFeature()
         features = QgsProcessingUtils.getFeatures(vlayerA, context)
diff --git a/python/plugins/processing/algs/qgis/ExecuteSQL.py b/python/plugins/processing/algs/qgis/ExecuteSQL.py
index 830c61f6430..13e4d7ed51c 100644
--- a/python/plugins/processing/algs/qgis/ExecuteSQL.py
+++ b/python/plugins/processing/algs/qgis/ExecuteSQL.py
@@ -145,7 +145,7 @@ class ExecuteSQL(GeoAlgorithm):
         if not vLayer.isValid():
             raise GeoAlgorithmExecutionException(vLayer.dataProvider().error().message())
 
-        writer = self.getOutputFromName(self.OUTPUT_LAYER).getVectorWriter(vLayer.fields().toList(),
+        writer = self.getOutputFromName(self.OUTPUT_LAYER).getVectorWriter(vLayer.fields(),
                                                                            vLayer.wkbType() if geometry_type != 1 else 1,
                                                                            vLayer.crs(), context)
 
diff --git a/python/plugins/processing/algs/qgis/ExportGeometryInfo.py b/python/plugins/processing/algs/qgis/ExportGeometryInfo.py
index 61c5ef2256c..6806f3c9e99 100644
--- a/python/plugins/processing/algs/qgis/ExportGeometryInfo.py
+++ b/python/plugins/processing/algs/qgis/ExportGeometryInfo.py
@@ -106,7 +106,7 @@ class ExportGeometryInfo(GeoAlgorithm):
                 zName = vector.createUniqueFieldName('mvalue', fields)
                 fields.append(QgsField(zName, QVariant.Double))
 
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fields.toList(), layer.wkbType(), layer.crs(),
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fields, layer.wkbType(), layer.crs(),
                                                                      context)
 
         ellips = None
diff --git a/python/plugins/processing/algs/qgis/ExtentFromLayer.py b/python/plugins/processing/algs/qgis/ExtentFromLayer.py
index 63091f84a81..e6ba56778ea 100644
--- a/python/plugins/processing/algs/qgis/ExtentFromLayer.py
+++ b/python/plugins/processing/algs/qgis/ExtentFromLayer.py
@@ -30,7 +30,13 @@ import os
 from qgis.PyQt.QtGui import QIcon
 from qgis.PyQt.QtCore import QVariant
 
-from qgis.core import QgsField, QgsPoint, QgsGeometry, QgsFeature, QgsWkbTypes, QgsProcessingUtils
+from qgis.core import (QgsField,
+                       QgsPoint,
+                       QgsGeometry,
+                       QgsFeature,
+                       QgsWkbTypes,
+                       QgsProcessingUtils,
+                       QgsFields)
 
 from processing.core.GeoAlgorithm import GeoAlgorithm
 from processing.core.parameters import ParameterVector
@@ -75,18 +81,17 @@ class ExtentFromLayer(GeoAlgorithm):
         layer = QgsProcessingUtils.mapLayerFromString(self.getParameterValue(self.INPUT_LAYER), context)
         byFeature = self.getParameterValue(self.BY_FEATURE)
 
-        fields = [
-            QgsField('MINX', QVariant.Double),
-            QgsField('MINY', QVariant.Double),
-            QgsField('MAXX', QVariant.Double),
-            QgsField('MAXY', QVariant.Double),
-            QgsField('CNTX', QVariant.Double),
-            QgsField('CNTY', QVariant.Double),
-            QgsField('AREA', QVariant.Double),
-            QgsField('PERIM', QVariant.Double),
-            QgsField('HEIGHT', QVariant.Double),
-            QgsField('WIDTH', QVariant.Double),
-        ]
+        fields = QgsFields()
+        fields.append(QgsField('MINX', QVariant.Double))
+        fields.append(QgsField('MINY', QVariant.Double))
+        fields.append(QgsField('MAXX', QVariant.Double))
+        fields.append(QgsField('MAXY', QVariant.Double))
+        fields.append(QgsField('CNTX', QVariant.Double))
+        fields.append(QgsField('CNTY', QVariant.Double))
+        fields.append(QgsField('AREA', QVariant.Double))
+        fields.append(QgsField('PERIM', QVariant.Double))
+        fields.append(QgsField('HEIGHT', QVariant.Double))
+        fields.append(QgsField('WIDTH', QVariant.Double))
 
         writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fields, QgsWkbTypes.Polygon, layer.crs(), context)
 
diff --git a/python/plugins/processing/algs/qgis/FieldsMapper.py b/python/plugins/processing/algs/qgis/FieldsMapper.py
index 0464d4ef83f..1f82af35a01 100644
--- a/python/plugins/processing/algs/qgis/FieldsMapper.py
+++ b/python/plugins/processing/algs/qgis/FieldsMapper.py
@@ -29,6 +29,7 @@ __copyright__ = '(C) 2014, Arnaud Morvan'
 __revision__ = '$Format:%H$'
 
 from qgis.core import (QgsField,
+                       QgsFields,
                        QgsExpression,
                        QgsDistanceArea,
                        QgsProject,
@@ -115,7 +116,7 @@ class FieldsMapper(GeoAlgorithm):
         output = self.getOutputFromName(self.OUTPUT_LAYER)
 
         layer = QgsProcessingUtils.mapLayerFromString(layer, context)
-        fields = []
+        fields = QgsFields()
         expressions = []
 
         da = QgsDistanceArea()
@@ -125,10 +126,10 @@ class FieldsMapper(GeoAlgorithm):
         exp_context = layer.createExpressionContext()
 
         for field_def in mapping:
-            fields.append(QgsField(name=field_def['name'],
-                                   type=field_def['type'],
-                                   len=field_def['length'],
-                                   prec=field_def['precision']))
+            fields.append(QgsField(field_def['name'],
+                                   field_def['type'],
+                                   field_def['length'],
+                                   field_def['precision']))
 
             expression = QgsExpression(field_def['expression'])
             expression.setGeomCalculator(da)
diff --git a/python/plugins/processing/algs/qgis/FixedDistanceBuffer.py b/python/plugins/processing/algs/qgis/FixedDistanceBuffer.py
index 047791f80da..0a08c7f5e2a 100644
--- a/python/plugins/processing/algs/qgis/FixedDistanceBuffer.py
+++ b/python/plugins/processing/algs/qgis/FixedDistanceBuffer.py
@@ -106,7 +106,7 @@ class FixedDistanceBuffer(GeoAlgorithm):
         miter_limit = self.getParameterValue(self.MITRE_LIMIT)
 
         writer = self.getOutputFromName(
-            self.OUTPUT).getVectorWriter(layer.fields().toList(), QgsWkbTypes.Polygon, layer.crs(), context)
+            self.OUTPUT).getVectorWriter(layer.fields(), QgsWkbTypes.Polygon, layer.crs(), context)
 
         buff.buffering(feedback, context, writer, distance, None, False, layer, dissolve, segments, end_cap_style,
                        join_style, miter_limit)
diff --git a/python/plugins/processing/algs/qgis/GridLine.py b/python/plugins/processing/algs/qgis/GridLine.py
index c620c61e63b..5cd9f14a61e 100644
--- a/python/plugins/processing/algs/qgis/GridLine.py
+++ b/python/plugins/processing/algs/qgis/GridLine.py
@@ -37,7 +37,8 @@ from qgis.core import (QgsRectangle,
                        QgsGeometry,
                        QgsPointV2,
                        QgsLineString,
-                       QgsWkbTypes)
+                       QgsWkbTypes,
+                       QgsFields)
 from processing.core.GeoAlgorithm import GeoAlgorithm
 from processing.core.GeoAlgorithmExecutionException import GeoAlgorithmExecutionException
 from processing.core.parameters import ParameterExtent
@@ -118,13 +119,13 @@ class GridLine(GeoAlgorithm):
             raise GeoAlgorithmExecutionException(
                 self.tr('Vertical spacing is too small for the covered area'))
 
-        fields = [QgsField('left', QVariant.Double, '', 24, 16),
-                  QgsField('top', QVariant.Double, '', 24, 16),
-                  QgsField('right', QVariant.Double, '', 24, 16),
-                  QgsField('bottom', QVariant.Double, '', 24, 16),
-                  QgsField('id', QVariant.Int, '', 10, 0),
-                  QgsField('coord', QVariant.Double, '', 24, 15)
-                  ]
+        fields = QgsFields()
+        fields.append(QgsField('left', QVariant.Double, '', 24, 16))
+        fields.append(QgsField('top', QVariant.Double, '', 24, 16))
+        fields.append(QgsField('right', QVariant.Double, '', 24, 16))
+        fields.append(QgsField('bottom', QVariant.Double, '', 24, 16))
+        fields.append(QgsField('id', QVariant.Int, '', 10, 0))
+        fields.append(QgsField('coord', QVariant.Double, '', 24, 15))
 
         writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fields, QgsWkbTypes.LineString, crs, context)
 
diff --git a/python/plugins/processing/algs/qgis/GridPolygon.py b/python/plugins/processing/algs/qgis/GridPolygon.py
index 4b5148da65c..5d0c895672d 100644
--- a/python/plugins/processing/algs/qgis/GridPolygon.py
+++ b/python/plugins/processing/algs/qgis/GridPolygon.py
@@ -30,7 +30,14 @@ import math
 
 from qgis.PyQt.QtGui import QIcon
 from qgis.PyQt.QtCore import QVariant
-from qgis.core import QgsRectangle, QgsCoordinateReferenceSystem, QgsField, QgsFeature, QgsGeometry, QgsPoint, QgsWkbTypes
+from qgis.core import (QgsRectangle,
+                       QgsCoordinateReferenceSystem,
+                       QgsField,
+                       QgsFeature,
+                       QgsGeometry,
+                       QgsPoint,
+                       QgsWkbTypes,
+                       QgsFields)
 
 from processing.core.GeoAlgorithm import GeoAlgorithm
 from processing.core.GeoAlgorithmExecutionException import GeoAlgorithmExecutionException
@@ -123,12 +130,12 @@ class GridPolygon(GeoAlgorithm):
             raise GeoAlgorithmExecutionException(
                 self.tr('Vertical spacing is too small for the covered area'))
 
-        fields = [QgsField('left', QVariant.Double, '', 24, 16),
-                  QgsField('top', QVariant.Double, '', 24, 16),
-                  QgsField('right', QVariant.Double, '', 24, 16),
-                  QgsField('bottom', QVariant.Double, '', 24, 16),
-                  QgsField('id', QVariant.Int, '', 10, 0)
-                  ]
+        fields = QgsFields()
+        fields.append(QgsField('left', QVariant.Double, '', 24, 16))
+        fields.append(QgsField('top', QVariant.Double, '', 24, 16))
+        fields.append(QgsField('right', QVariant.Double, '', 24, 16))
+        fields.append(QgsField('bottom', QVariant.Double, '', 24, 16))
+        fields.append(QgsField('id', QVariant.Int, '', 10, 0))
 
         writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fields, QgsWkbTypes.Polygon, crs, context)
 
diff --git a/python/plugins/processing/algs/qgis/LinesIntersection.py b/python/plugins/processing/algs/qgis/LinesIntersection.py
index 91d148e8b7a..2dae2336be4 100644
--- a/python/plugins/processing/algs/qgis/LinesIntersection.py
+++ b/python/plugins/processing/algs/qgis/LinesIntersection.py
@@ -103,7 +103,8 @@ class LinesIntersection(GeoAlgorithm):
             fieldListB = layerB.fields()
 
         fieldListB = vector.testForUniqueness(fieldListA, fieldListB)
-        fieldListA.extend(fieldListB)
+        for b in fieldListB:
+            fieldListA.append(b)
 
         writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fieldListA, QgsWkbTypes.Point, layerA.crs(),
                                                                      context)
diff --git a/python/plugins/processing/algs/qgis/LinesToPolygons.py b/python/plugins/processing/algs/qgis/LinesToPolygons.py
index ce2aa57bc77..e1aff329453 100644
--- a/python/plugins/processing/algs/qgis/LinesToPolygons.py
+++ b/python/plugins/processing/algs/qgis/LinesToPolygons.py
@@ -68,7 +68,7 @@ class LinesToPolygons(GeoAlgorithm):
     def processAlgorithm(self, context, feedback):
         layer = QgsProcessingUtils.mapLayerFromString(self.getParameterValue(self.INPUT), context)
 
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields().toList(), QgsWkbTypes.Polygon,
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields(), QgsWkbTypes.Polygon,
                                                                      layer.crs(), context)
 
         outFeat = QgsFeature()
diff --git a/python/plugins/processing/algs/qgis/MeanCoords.py b/python/plugins/processing/algs/qgis/MeanCoords.py
index 19dd168291e..cedaf439fbc 100644
--- a/python/plugins/processing/algs/qgis/MeanCoords.py
+++ b/python/plugins/processing/algs/qgis/MeanCoords.py
@@ -93,9 +93,10 @@ class MeanCoords(GeoAlgorithm):
         else:
             uniqueIndex = layer.fields().lookupField(uniqueField)
 
-        fieldList = [QgsField('MEAN_X', QVariant.Double, '', 24, 15),
-                     QgsField('MEAN_Y', QVariant.Double, '', 24, 15),
-                     QgsField('UID', QVariant.String, '', 255)]
+        fieldList = QgsFields()
+        fieldList.append(QgsField('MEAN_X', QVariant.Double, '', 24, 15))
+        fieldList.append(QgsField('MEAN_Y', QVariant.Double, '', 24, 15))
+        fieldList.append(QgsField('UID', QVariant.String, '', 255))
 
         writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fieldList, QgsWkbTypes.Point, layer.crs(), context)
 
diff --git a/python/plugins/processing/algs/qgis/Merge.py b/python/plugins/processing/algs/qgis/Merge.py
index cb025c8372b..868c2412add 100644
--- a/python/plugins/processing/algs/qgis/Merge.py
+++ b/python/plugins/processing/algs/qgis/Merge.py
@@ -95,7 +95,7 @@ class Merge(GeoAlgorithm):
                     fields.append(sfield)
 
         total = 100.0 / totalFeatureCount
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fields.toList(), layers[0].wkbType(),
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fields, layers[0].wkbType(),
                                                                      layers[0].crs(), context)
 
         featureCount = 0
diff --git a/python/plugins/processing/algs/qgis/MergeLines.py b/python/plugins/processing/algs/qgis/MergeLines.py
index 3b956f5b7ad..5d3858a89a4 100644
--- a/python/plugins/processing/algs/qgis/MergeLines.py
+++ b/python/plugins/processing/algs/qgis/MergeLines.py
@@ -69,7 +69,7 @@ class MergeLines(GeoAlgorithm):
         layer = QgsProcessingUtils.mapLayerFromString(self.getParameterValue(self.INPUT_LAYER), context)
 
         writer = self.getOutputFromName(
-            self.OUTPUT_LAYER).getVectorWriter(layer.fields().toList(), layer.wkbType(), layer.crs(), context)
+            self.OUTPUT_LAYER).getVectorWriter(layer.fields(), layer.wkbType(), layer.crs(), context)
 
         features = QgsProcessingUtils.getFeatures(layer, context)
         total = 100.0 / QgsProcessingUtils.featureCount(layer, context)
diff --git a/python/plugins/processing/algs/qgis/MultipartToSingleparts.py b/python/plugins/processing/algs/qgis/MultipartToSingleparts.py
index a22bbb44740..36a76cdf036 100644
--- a/python/plugins/processing/algs/qgis/MultipartToSingleparts.py
+++ b/python/plugins/processing/algs/qgis/MultipartToSingleparts.py
@@ -63,7 +63,7 @@ class MultipartToSingleparts(GeoAlgorithm):
         layer = QgsProcessingUtils.mapLayerFromString(self.getParameterValue(self.INPUT), context)
         geomType = QgsWkbTypes.singleType(layer.wkbType())
 
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields().toList(), geomType, layer.crs(),
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields(), geomType, layer.crs(),
                                                                      context)
 
         features = QgsProcessingUtils.getFeatures(layer, context)
diff --git a/python/plugins/processing/algs/qgis/OffsetLine.py b/python/plugins/processing/algs/qgis/OffsetLine.py
index 1dec31d8440..2d1ea8260df 100644
--- a/python/plugins/processing/algs/qgis/OffsetLine.py
+++ b/python/plugins/processing/algs/qgis/OffsetLine.py
@@ -87,7 +87,7 @@ class OffsetLine(GeoAlgorithm):
         layer = QgsProcessingUtils.mapLayerFromString(self.getParameterValue(self.INPUT_LAYER), context)
 
         writer = self.getOutputFromName(
-            self.OUTPUT_LAYER).getVectorWriter(layer.fields().toList(), QgsWkbTypes.LineString, layer.crs(), context)
+            self.OUTPUT_LAYER).getVectorWriter(layer.fields(), QgsWkbTypes.LineString, layer.crs(), context)
 
         distance = self.getParameterValue(self.DISTANCE)
         segments = int(self.getParameterValue(self.SEGMENTS))
diff --git a/python/plugins/processing/algs/qgis/PointOnSurface.py b/python/plugins/processing/algs/qgis/PointOnSurface.py
index 171e2cc600e..4b867d3ae9a 100644
--- a/python/plugins/processing/algs/qgis/PointOnSurface.py
+++ b/python/plugins/processing/algs/qgis/PointOnSurface.py
@@ -66,7 +66,7 @@ class PointOnSurface(GeoAlgorithm):
         layer = QgsProcessingUtils.mapLayerFromString(self.getParameterValue(self.INPUT_LAYER), context)
 
         writer = self.getOutputFromName(
-            self.OUTPUT_LAYER).getVectorWriter(layer.fields().toList(), QgsWkbTypes.Point, layer.crs(), context)
+            self.OUTPUT_LAYER).getVectorWriter(layer.fields(), QgsWkbTypes.Point, layer.crs(), context)
 
         features = QgsProcessingUtils.getFeatures(layer, context)
         total = 100.0 / QgsProcessingUtils.featureCount(layer, context)
diff --git a/python/plugins/processing/algs/qgis/PointsFromLines.py b/python/plugins/processing/algs/qgis/PointsFromLines.py
index a151c06533a..f7febc51a7e 100644
--- a/python/plugins/processing/algs/qgis/PointsFromLines.py
+++ b/python/plugins/processing/algs/qgis/PointsFromLines.py
@@ -87,7 +87,7 @@ class PointsFromLines(GeoAlgorithm):
         fields.append(QgsField('line_id', QVariant.Int, '', 10, 0))
         fields.append(QgsField('point_id', QVariant.Int, '', 10, 0))
 
-        writer = self.getOutputFromName(self.OUTPUT_LAYER).getVectorWriter(fields.toList(), QgsWkbTypes.Point,
+        writer = self.getOutputFromName(self.OUTPUT_LAYER).getVectorWriter(fields, QgsWkbTypes.Point,
                                                                            layer.crs(), context)
 
         outFeature = QgsFeature()
diff --git a/python/plugins/processing/algs/qgis/PointsFromPolygons.py b/python/plugins/processing/algs/qgis/PointsFromPolygons.py
index 3163b452ff0..e217dca307a 100644
--- a/python/plugins/processing/algs/qgis/PointsFromPolygons.py
+++ b/python/plugins/processing/algs/qgis/PointsFromPolygons.py
@@ -87,7 +87,7 @@ class PointsFromPolygons(GeoAlgorithm):
         fields.append(QgsField('poly_id', QVariant.Int, '', 10, 0))
         fields.append(QgsField('point_id', QVariant.Int, '', 10, 0))
 
-        writer = self.getOutputFromName(self.OUTPUT_LAYER).getVectorWriter(fields.toList(), QgsWkbTypes.Point,
+        writer = self.getOutputFromName(self.OUTPUT_LAYER).getVectorWriter(fields, QgsWkbTypes.Point,
                                                                            layer.crs(), context)
 
         outFeature = QgsFeature()
diff --git a/python/plugins/processing/algs/qgis/PointsInPolygon.py b/python/plugins/processing/algs/qgis/PointsInPolygon.py
index 9ca26f46b0d..db4a95fbeac 100644
--- a/python/plugins/processing/algs/qgis/PointsInPolygon.py
+++ b/python/plugins/processing/algs/qgis/PointsInPolygon.py
@@ -80,7 +80,7 @@ class PointsInPolygon(GeoAlgorithm):
         (idxCount, fieldList) = vector.findOrCreateField(polyLayer,
                                                          polyLayer.fields(), fieldName)
 
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fields.toList(), polyLayer.wkbType(),
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fields, polyLayer.wkbType(),
                                                                      polyLayer.crs(), context)
 
         spatialIndex = QgsProcessingUtils.createSpatialIndex(pointLayer, context)
diff --git a/python/plugins/processing/algs/qgis/PointsInPolygonUnique.py b/python/plugins/processing/algs/qgis/PointsInPolygonUnique.py
index 86b19152ad9..d19ff812660 100644
--- a/python/plugins/processing/algs/qgis/PointsInPolygonUnique.py
+++ b/python/plugins/processing/algs/qgis/PointsInPolygonUnique.py
@@ -87,7 +87,7 @@ class PointsInPolygonUnique(GeoAlgorithm):
         (idxCount, fieldList) = vector.findOrCreateField(polyLayer,
                                                          polyLayer.fields(), fieldName)
 
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fields.toList(), polyLayer.wkbType(),
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fields, polyLayer.wkbType(),
                                                                      polyLayer.crs(), context)
 
         spatialIndex = QgsProcessingUtils.createSpatialIndex(pointLayer, context)
diff --git a/python/plugins/processing/algs/qgis/PointsInPolygonWeighted.py b/python/plugins/processing/algs/qgis/PointsInPolygonWeighted.py
index 4a35ca573fe..0838137de6b 100644
--- a/python/plugins/processing/algs/qgis/PointsInPolygonWeighted.py
+++ b/python/plugins/processing/algs/qgis/PointsInPolygonWeighted.py
@@ -93,7 +93,7 @@ class PointsInPolygonWeighted(GeoAlgorithm):
         (idxCount, fieldList) = vector.findOrCreateField(polyLayer,
                                                          polyLayer.fields(), fieldName)
 
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fields.toList(), polyLayer.wkbType(),
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fields, polyLayer.wkbType(),
                                                                      polyLayer.crs(), context)
 
         spatialIndex = QgsProcessingUtils.createSpatialIndex(pointLayer, context)
diff --git a/python/plugins/processing/algs/qgis/PolygonsToLines.py b/python/plugins/processing/algs/qgis/PolygonsToLines.py
index 8944ce71628..a59e1df609c 100644
--- a/python/plugins/processing/algs/qgis/PolygonsToLines.py
+++ b/python/plugins/processing/algs/qgis/PolygonsToLines.py
@@ -68,7 +68,7 @@ class PolygonsToLines(GeoAlgorithm):
     def processAlgorithm(self, context, feedback):
         layer = QgsProcessingUtils.mapLayerFromString(self.getParameterValue(self.INPUT), context)
 
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields().toList(), QgsWkbTypes.LineString,
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields(), QgsWkbTypes.LineString,
                                                                      layer.crs(), context)
 
         features = QgsProcessingUtils.getFeatures(layer, context)
diff --git a/python/plugins/processing/algs/qgis/RandomExtract.py b/python/plugins/processing/algs/qgis/RandomExtract.py
index 62001f782af..3353551ded9 100644
--- a/python/plugins/processing/algs/qgis/RandomExtract.py
+++ b/python/plugins/processing/algs/qgis/RandomExtract.py
@@ -96,7 +96,7 @@ class RandomExtract(GeoAlgorithm):
 
         selran = random.sample(list(range(featureCount)), value)
 
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields().toList(), layer.wkbType(),
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields(), layer.wkbType(),
                                                                      layer.crs(), context)
 
         total = 100.0 / featureCount
diff --git a/python/plugins/processing/algs/qgis/RandomExtractWithinSubsets.py b/python/plugins/processing/algs/qgis/RandomExtractWithinSubsets.py
index 80eccf4dc79..bb4fc703863 100644
--- a/python/plugins/processing/algs/qgis/RandomExtractWithinSubsets.py
+++ b/python/plugins/processing/algs/qgis/RandomExtractWithinSubsets.py
@@ -103,7 +103,7 @@ class RandomExtractWithinSubsets(GeoAlgorithm):
                             "correct value and try again."))
             value = value / 100.0
 
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields().toList(), layer.wkbType(),
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields(), layer.wkbType(),
                                                                      layer.crs(), context)
 
         selran = []
diff --git a/python/plugins/processing/algs/qgis/RectanglesOvalsDiamondsFixed.py b/python/plugins/processing/algs/qgis/RectanglesOvalsDiamondsFixed.py
index e374bc96ce8..441768066ff 100644
--- a/python/plugins/processing/algs/qgis/RectanglesOvalsDiamondsFixed.py
+++ b/python/plugins/processing/algs/qgis/RectanglesOvalsDiamondsFixed.py
@@ -101,7 +101,7 @@ class RectanglesOvalsDiamondsFixed(GeoAlgorithm):
         segments = self.getParameterValue(self.SEGMENTS)
 
         writer = self.getOutputFromName(
-            self.OUTPUT_LAYER).getVectorWriter(layer.fields().toList(), QgsWkbTypes.Polygon, layer.crs(), context)
+            self.OUTPUT_LAYER).getVectorWriter(layer.fields(), QgsWkbTypes.Polygon, layer.crs(), context)
 
         features = QgsProcessingUtils.getFeatures(layer, context)
 
diff --git a/python/plugins/processing/algs/qgis/RectanglesOvalsDiamondsVariable.py b/python/plugins/processing/algs/qgis/RectanglesOvalsDiamondsVariable.py
index 3157b4e79f4..3a54d32b6c9 100644
--- a/python/plugins/processing/algs/qgis/RectanglesOvalsDiamondsVariable.py
+++ b/python/plugins/processing/algs/qgis/RectanglesOvalsDiamondsVariable.py
@@ -110,7 +110,7 @@ class RectanglesOvalsDiamondsVariable(GeoAlgorithm):
         segments = self.getParameterValue(self.SEGMENTS)
 
         writer = self.getOutputFromName(
-            self.OUTPUT_LAYER).getVectorWriter(layer.fields().toList(), QgsWkbTypes.Polygon, layer.crs(), context)
+            self.OUTPUT_LAYER).getVectorWriter(layer.fields(), QgsWkbTypes.Polygon, layer.crs(), context)
 
         features = QgsProcessingUtils.getFeatures(layer, context)
 
diff --git a/python/plugins/processing/algs/qgis/ReprojectLayer.py b/python/plugins/processing/algs/qgis/ReprojectLayer.py
index c3f4e28b77f..aa7d3dd18fc 100644
--- a/python/plugins/processing/algs/qgis/ReprojectLayer.py
+++ b/python/plugins/processing/algs/qgis/ReprojectLayer.py
@@ -72,7 +72,7 @@ class ReprojectLayer(GeoAlgorithm):
         targetCrs = QgsCoordinateReferenceSystem()
         targetCrs.createFromUserInput(crsId)
 
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields().toList(), layer.wkbType(),
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields(), layer.wkbType(),
                                                                      targetCrs, context)
 
         layerCrs = layer.crs()
diff --git a/python/plugins/processing/algs/qgis/ReverseLineDirection.py b/python/plugins/processing/algs/qgis/ReverseLineDirection.py
index 37312ed5953..8013a1a6f52 100644
--- a/python/plugins/processing/algs/qgis/ReverseLineDirection.py
+++ b/python/plugins/processing/algs/qgis/ReverseLineDirection.py
@@ -65,7 +65,7 @@ class ReverseLineDirection(GeoAlgorithm):
         layer = QgsProcessingUtils.mapLayerFromString(self.getParameterValue(self.INPUT_LAYER), context)
 
         writer = self.getOutputFromName(
-            self.OUTPUT_LAYER).getVectorWriter(layer.fields().toList(), layer.wkbType(), layer.crs(), context)
+            self.OUTPUT_LAYER).getVectorWriter(layer.fields(), layer.wkbType(), layer.crs(), context)
 
         outFeat = QgsFeature()
 
diff --git a/python/plugins/processing/algs/qgis/ShortestPathLayerToPoint.py b/python/plugins/processing/algs/qgis/ShortestPathLayerToPoint.py
index 6bdec281866..94bc8ff3c48 100644
--- a/python/plugins/processing/algs/qgis/ShortestPathLayerToPoint.py
+++ b/python/plugins/processing/algs/qgis/ShortestPathLayerToPoint.py
@@ -180,7 +180,7 @@ class ShortestPathLayerToPoint(GeoAlgorithm):
         feat.setFields(fields)
 
         writer = self.getOutputFromName(
-            self.OUTPUT_LAYER).getVectorWriter(fields.toList(), QgsWkbTypes.LineString, layer.crs(), context)
+            self.OUTPUT_LAYER).getVectorWriter(fields, QgsWkbTypes.LineString, layer.crs(), context)
 
         tmp = endPoint.split(',')
         endPoint = QgsPoint(float(tmp[0]), float(tmp[1]))
diff --git a/python/plugins/processing/algs/qgis/ShortestPathPointToLayer.py b/python/plugins/processing/algs/qgis/ShortestPathPointToLayer.py
index fa90763f1b4..ee6a46cdbea 100644
--- a/python/plugins/processing/algs/qgis/ShortestPathPointToLayer.py
+++ b/python/plugins/processing/algs/qgis/ShortestPathPointToLayer.py
@@ -173,7 +173,7 @@ class ShortestPathPointToLayer(GeoAlgorithm):
         feat.setFields(fields)
 
         writer = self.getOutputFromName(
-            self.OUTPUT_LAYER).getVectorWriter(fields.toList(), QgsWkbTypes.LineString, layer.crs(), context)
+            self.OUTPUT_LAYER).getVectorWriter(fields, QgsWkbTypes.LineString, layer.crs(), context)
 
         tmp = startPoint.split(',')
         startPoint = QgsPoint(float(tmp[0]), float(tmp[1]))
diff --git a/python/plugins/processing/algs/qgis/ShortestPathPointToPoint.py b/python/plugins/processing/algs/qgis/ShortestPathPointToPoint.py
index f2658bf76e6..51d8a14c8c1 100644
--- a/python/plugins/processing/algs/qgis/ShortestPathPointToPoint.py
+++ b/python/plugins/processing/algs/qgis/ShortestPathPointToPoint.py
@@ -180,7 +180,7 @@ class ShortestPathPointToPoint(GeoAlgorithm):
         fields.append(QgsField('cost', QVariant.Double, '', 20, 7))
 
         writer = self.getOutputFromName(
-            self.OUTPUT_LAYER).getVectorWriter(fields.toList(), QgsWkbTypes.LineString, layer.crs(), context)
+            self.OUTPUT_LAYER).getVectorWriter(fields, QgsWkbTypes.LineString, layer.crs(), context)
 
         tmp = startPoint.split(',')
         startPoint = QgsPoint(float(tmp[0]), float(tmp[1]))
diff --git a/python/plugins/processing/algs/qgis/SimplifyGeometries.py b/python/plugins/processing/algs/qgis/SimplifyGeometries.py
index f52f8e6ecdc..f08be004612 100644
--- a/python/plugins/processing/algs/qgis/SimplifyGeometries.py
+++ b/python/plugins/processing/algs/qgis/SimplifyGeometries.py
@@ -86,7 +86,7 @@ class SimplifyGeometries(GeoAlgorithm):
         pointsBefore = 0
         pointsAfter = 0
 
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields().toList(), layer.wkbType(),
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields(), layer.wkbType(),
                                                                      layer.crs(), context)
 
         features = QgsProcessingUtils.getFeatures(layer, context)
diff --git a/python/plugins/processing/algs/qgis/SinglePartsToMultiparts.py b/python/plugins/processing/algs/qgis/SinglePartsToMultiparts.py
index 3bffa6d7ed5..ac10ad28750 100644
--- a/python/plugins/processing/algs/qgis/SinglePartsToMultiparts.py
+++ b/python/plugins/processing/algs/qgis/SinglePartsToMultiparts.py
@@ -71,7 +71,7 @@ class SinglePartsToMultiparts(GeoAlgorithm):
 
         geomType = QgsWkbTypes.multiType(layer.wkbType())
 
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields().toList(), geomType, layer.crs(),
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields(), geomType, layer.crs(),
                                                                      context)
 
         outFeat = QgsFeature()
diff --git a/python/plugins/processing/algs/qgis/SingleSidedBuffer.py b/python/plugins/processing/algs/qgis/SingleSidedBuffer.py
index 196735d0680..251366a7f80 100644
--- a/python/plugins/processing/algs/qgis/SingleSidedBuffer.py
+++ b/python/plugins/processing/algs/qgis/SingleSidedBuffer.py
@@ -97,7 +97,7 @@ class SingleSidedBuffer(GeoAlgorithm):
         layer = QgsProcessingUtils.mapLayerFromString(self.getParameterValue(self.INPUT_LAYER), context)
 
         writer = self.getOutputFromName(
-            self.OUTPUT_LAYER).getVectorWriter(layer.fields().toList(), QgsWkbTypes.Polygon, layer.crs(), context)
+            self.OUTPUT_LAYER).getVectorWriter(layer.fields(), QgsWkbTypes.Polygon, layer.crs(), context)
 
         distance = self.getParameterValue(self.DISTANCE)
         segments = int(self.getParameterValue(self.SEGMENTS))
diff --git a/python/plugins/processing/algs/qgis/Smooth.py b/python/plugins/processing/algs/qgis/Smooth.py
index 1896176acdd..1a8f612b97e 100644
--- a/python/plugins/processing/algs/qgis/Smooth.py
+++ b/python/plugins/processing/algs/qgis/Smooth.py
@@ -75,7 +75,7 @@ class Smooth(GeoAlgorithm):
         max_angle = self.getParameterValue(self.MAX_ANGLE)
 
         writer = self.getOutputFromName(
-            self.OUTPUT_LAYER).getVectorWriter(layer.fields().toList(), layer.wkbType(), layer.crs(), context)
+            self.OUTPUT_LAYER).getVectorWriter(layer.fields(), layer.wkbType(), layer.crs(), context)
 
         features = QgsProcessingUtils.getFeatures(layer, context)
         total = 100.0 / QgsProcessingUtils.featureCount(layer, context)
diff --git a/python/plugins/processing/algs/qgis/SumLines.py b/python/plugins/processing/algs/qgis/SumLines.py
index 7e0dbf96d23..ef6f1f132db 100644
--- a/python/plugins/processing/algs/qgis/SumLines.py
+++ b/python/plugins/processing/algs/qgis/SumLines.py
@@ -83,7 +83,7 @@ class SumLines(GeoAlgorithm):
         (idxCount, fieldList) = vector.findOrCreateField(polyLayer, fieldList,
                                                          countFieldName)
 
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fieldList.toList(), polyLayer.wkbType(),
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(fieldList, polyLayer.wkbType(),
                                                                      polyLayer.crs(), context)
 
         spatialIndex = QgsProcessingUtils.createSpatialIndex(lineLayer, context)
diff --git a/python/plugins/processing/algs/qgis/Translate.py b/python/plugins/processing/algs/qgis/Translate.py
index f7ff102a748..246c91b2bea 100644
--- a/python/plugins/processing/algs/qgis/Translate.py
+++ b/python/plugins/processing/algs/qgis/Translate.py
@@ -73,7 +73,7 @@ class Translate(GeoAlgorithm):
         layer = QgsProcessingUtils.mapLayerFromString(self.getParameterValue(self.INPUT_LAYER), context)
 
         writer = self.getOutputFromName(
-            self.OUTPUT_LAYER).getVectorWriter(layer.fields().toList(), layer.wkbType(), layer.crs(), context)
+            self.OUTPUT_LAYER).getVectorWriter(layer.fields(), layer.wkbType(), layer.crs(), context)
 
         delta_x = self.getParameterValue(self.DELTA_X)
         delta_y = self.getParameterValue(self.DELTA_Y)
diff --git a/python/plugins/processing/algs/qgis/VariableDistanceBuffer.py b/python/plugins/processing/algs/qgis/VariableDistanceBuffer.py
index 6c9627c8963..33a7ce8a8ab 100644
--- a/python/plugins/processing/algs/qgis/VariableDistanceBuffer.py
+++ b/python/plugins/processing/algs/qgis/VariableDistanceBuffer.py
@@ -82,7 +82,7 @@ class VariableDistanceBuffer(GeoAlgorithm):
         field = self.getParameterValue(self.FIELD)
         segments = int(self.getParameterValue(self.SEGMENTS))
 
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields().toList(), QgsWkbTypes.Polygon,
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields(), QgsWkbTypes.Polygon,
                                                                      layer.crs(), context)
 
         buff.buffering(feedback, context, writer, 0, field, True, layer, dissolve, segments)
diff --git a/python/plugins/processing/algs/qgis/VoronoiPolygons.py b/python/plugins/processing/algs/qgis/VoronoiPolygons.py
index 518ba69e8bb..99c85847260 100644
--- a/python/plugins/processing/algs/qgis/VoronoiPolygons.py
+++ b/python/plugins/processing/algs/qgis/VoronoiPolygons.py
@@ -75,7 +75,7 @@ class VoronoiPolygons(GeoAlgorithm):
 
         buf = self.getParameterValue(self.BUFFER)
 
-        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields().toList(), QgsWkbTypes.Polygon,
+        writer = self.getOutputFromName(self.OUTPUT).getVectorWriter(layer.fields(), QgsWkbTypes.Polygon,
                                                                      layer.crs(), context)
 
         outFeat = QgsFeature()
diff --git a/python/plugins/processing/algs/qgis/ZonalStatistics.py b/python/plugins/processing/algs/qgis/ZonalStatistics.py
index c99a65c7e49..4e5c8d5f16d 100644
--- a/python/plugins/processing/algs/qgis/ZonalStatistics.py
+++ b/python/plugins/processing/algs/qgis/ZonalStatistics.py
@@ -176,7 +176,7 @@ class ZonalStatistics(GeoAlgorithm):
             (idxMode, fields) = vector.findOrCreateField(layer, fields,
                                                          columnPrefix + 'mode', 21, 6)
 
-        writer = self.getOutputFromName(self.OUTPUT_LAYER).getVectorWriter(fields.toList(), layer.wkbType(),
+        writer = self.getOutputFromName(self.OUTPUT_LAYER).getVectorWriter(fields, layer.wkbType(),
                                                                            layer.crs(), context)
 
         outFeat = QgsFeature()
diff --git a/python/plugins/processing/tools/vector.py b/python/plugins/processing/tools/vector.py
index 342123178d3..293df7e488b 100644
--- a/python/plugins/processing/tools/vector.py
+++ b/python/plugins/processing/tools/vector.py
@@ -280,7 +280,10 @@ def combineVectorFields(layerA, layerB):
             field = QgsField(newName, field.type(), field.typeName())
         fields.append(field)
 
-    return fields
+    real_fields = QgsFields()
+    for f in fields:
+        real_fields.append(f)
+    return real_fields
 
 
 def checkMinDistance(point, index, distance, points):