From 9ae156970a124992bb8d4c1767831e433e284b00 Mon Sep 17 00:00:00 2001
From: Even Rouault <even.rouault@spatialys.com>
Date: Tue, 18 Oct 2016 22:32:56 +0200
Subject: [PATCH] QgsVectorLayer::writeSymbology(): fix crash when called with
 invalid data provider

---
 src/core/qgsvectorlayer.cpp | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/core/qgsvectorlayer.cpp b/src/core/qgsvectorlayer.cpp
index 7f7472432f6..173c1e60a1f 100644
--- a/src/core/qgsvectorlayer.cpp
+++ b/src/core/qgsvectorlayer.cpp
@@ -1947,7 +1947,14 @@ bool QgsVectorLayer::writeSymbology( QDomNode& node, QDomDocument& doc, QString&
   mConditionalStyles->writeXml( node, doc );
 
   // save expression fields
-  mExpressionFieldBuffer->writeXml( node, doc );
+  if ( !mExpressionFieldBuffer )
+  {
+    // can happen when saving style on a invalid layer
+    QgsExpressionFieldBuffer dummy;
+    dummy.writeXml( node, doc );
+  }
+  else
+    mExpressionFieldBuffer->writeXml( node, doc );
 
   // save readonly state
   node.toElement().setAttribute( QStringLiteral( "readOnly" ), mReadOnly );