Add method to test if QgsMapUnitScale is null

python/PyQt6/core/auto_generated/qgsmapunitscale.sip.in

@@ -36,6 +36,14 @@ Constructor for QgsMapUnitScale
                  1000.0 for a 1:1000 map.
 %End
 
+    bool isNull() const;
+%Docstring
+Returns ``True`` if the scale is null, i.e. it is a default constructed
+QgsMapUnitScale.
+
+.. versionadded:: 3.44
+%End
+
     double minScale;
 
     double maxScale;

python/core/auto_generated/qgsmapunitscale.sip.in

@@ -36,6 +36,14 @@ Constructor for QgsMapUnitScale
                  1000.0 for a 1:1000 map.
 %End
 
+    bool isNull() const;
+%Docstring
+Returns ``True`` if the scale is null, i.e. it is a default constructed
+QgsMapUnitScale.
+
+.. versionadded:: 3.44
+%End
+
     double minScale;
 
     double maxScale;

src/core/qgsmapunitscale.cpp

@@ -17,6 +17,16 @@
 #include "qgsmapunitscale.h"
 #include "qgsrendercontext.h"
 
+bool QgsMapUnitScale::isNull() const
+{
+  return qgsDoubleNear( minScale, 0 )
+         && qgsDoubleNear( maxScale, 0 )
+         && !minSizeMMEnabled
+         && qgsDoubleNear( minSizeMM, 0 )
+         && !maxSizeMMEnabled
+         && qgsDoubleNear( maxSizeMM, 0 );
+}
+
 double QgsMapUnitScale::computeMapUnitsPerPixel( const QgsRenderContext &c ) const
 {
   double mup = c.mapToPixel().mapUnitsPerPixel();

src/core/qgsmapunitscale.h

@@ -48,6 +48,13 @@ class CORE_EXPORT QgsMapUnitScale
       , maxScale( maxScale )
     {}
 
+    /**
+     * Returns TRUE if the scale is null, i.e. it is a default constructed QgsMapUnitScale.
+     *
+     * \since QGIS 3.44
+     */
+    bool isNull() const;
+
     /**
      * The minimum scale, or 0.0 if unset.
      * The scale value indicates the scale denominator, e.g. 1000.0 for a 1:1000 map.

tests/src/python/test_qgsmapunitscale.py

@@ -74,6 +74,35 @@ class PyQgsMapUnitScale(unittest.TestCase):
 
         self.assertEqual(c1, c2)
 
+    def testIsNull(self):
+        # test isNull
+        c1 = QgsMapUnitScale()
+        self.assertTrue(c1.isNull())
+
+        c1 = QgsMapUnitScale()
+        c1.minScale = 1000
+        self.assertFalse(c1.isNull())
+
+        c1 = QgsMapUnitScale()
+        c1.maxScale = 1000
+        self.assertFalse(c1.isNull())
+
+        c1 = QgsMapUnitScale()
+        c1.minSizeMMEnabled = True
+        self.assertFalse(c1.isNull())
+
+        c1 = QgsMapUnitScale()
+        c1.maxSizeMMEnabled = True
+        self.assertFalse(c1.isNull())
+
+        c1 = QgsMapUnitScale()
+        c1.minSizeMM = 3
+        self.assertFalse(c1.isNull())
+
+        c1 = QgsMapUnitScale()
+        c1.maxSizeMM = 3
+        self.assertFalse(c1.isNull())
+
     def testMapUnitsPerPixel(self):
         # test computeMapUnitsPerPixel