From dbfa13bba970d7a3ea2861305349d2c7342ad78c Mon Sep 17 00:00:00 2001
From: Sandro Santilli <strk@kbt.io>
Date: Mon, 17 Oct 2022 16:29:36 +0200
Subject: [PATCH] Fix crash on empty polygon conversion to curve

Closes GH-50466 in 3.22 branch

Includes unit test
---
 src/core/geometry/qgspolygon.cpp           | 11 +++++++----
 tests/src/core/geometry/testqgspolygon.cpp |  5 ++++-
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/src/core/geometry/qgspolygon.cpp b/src/core/geometry/qgspolygon.cpp
index 104279704b74..6f46c70eca51 100644
--- a/src/core/geometry/qgspolygon.cpp
+++ b/src/core/geometry/qgspolygon.cpp
@@ -316,11 +316,14 @@ QgsPolygon *QgsPolygon::surfaceToPolygon() const
 QgsCurvePolygon *QgsPolygon::toCurveType() const
 {
   QgsCurvePolygon *curvePolygon = new QgsCurvePolygon();
-  curvePolygon->setExteriorRing( mExteriorRing->clone() );
-  int nInteriorRings = mInteriorRings.size();
-  for ( int i = 0; i < nInteriorRings; ++i )
+  if ( mExteriorRing )
   {
-    curvePolygon->addInteriorRing( mInteriorRings.at( i )->clone() );
+    curvePolygon->setExteriorRing( mExteriorRing->clone() );
+    int nInteriorRings = mInteriorRings.size();
+    for ( int i = 0; i < nInteriorRings; ++i )
+    {
+      curvePolygon->addInteriorRing( mInteriorRings.at( i )->clone() );
+    }
   }
   return curvePolygon;
 }
diff --git a/tests/src/core/geometry/testqgspolygon.cpp b/tests/src/core/geometry/testqgspolygon.cpp
index 70cb31551fc6..e472a7bb20f5 100644
--- a/tests/src/core/geometry/testqgspolygon.cpp
+++ b/tests/src/core/geometry/testqgspolygon.cpp
@@ -592,7 +592,10 @@ void TestQgsPolygon::polygon()
   QCOMPARE( *toP, p12 );
 
   //toCurveType
-  std::unique_ptr< QgsCurvePolygon > curveType( p12.toCurveType() );
+  std::unique_ptr< QgsCurvePolygon > curveType( QgsPolygon().toCurveType() );
+  QCOMPARE( curveType->wkbType(), QgsWkbTypes::CurvePolygon );
+
+  curveType.reset( p12.toCurveType() );
   QCOMPARE( curveType->wkbType(), QgsWkbTypes::CurvePolygonZM );
   QCOMPARE( curveType->exteriorRing()->numPoints(), 5 );
   QCOMPARE( curveType->exteriorRing()->vertexAt( QgsVertexId( 0, 0, 0 ) ), QgsPoint( QgsWkbTypes::PointZM, 0, 0, 1, 5 ) );