Fix #1709: NullPropagationTransform.IsGetter on generic types

ICSharpCode.Decompiler.Tests/TestCases/Pretty/NullPropagation.cs

@@ -17,6 +17,8 @@
 // DEALINGS IN THE SOFTWARE.
 
 using System;
+using System.Collections;
+using System.Collections.Generic;
 
 namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 {
@@ -258,6 +260,11 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			return t?.Int();
 		}
 
+		public int? Issue1709(object obj)
+		{
+			return (obj as ICollection)?.Count + (obj as ICollection<int>)?.Count;
+		}
+
 		private static dynamic DynamicNullProp(dynamic a)
 		{
 			return a?.b.c(1)?.d[10];

ICSharpCode.Decompiler/CSharp/StatementBuilder.cs

@@ -791,7 +791,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		bool ParentIsCurrentGetter(ILInstruction inst)
 		{
 			return inst.Parent is CallInstruction cv && cv.Method.IsAccessor &&
-				cv.Method.AccessorOwner is IProperty p && p.Getter.Equals(cv.Method);
+				cv.Method.AccessorKind == System.Reflection.MethodSemanticsAttributes.Getter;
 		}
 		#endregion
 

ICSharpCode.Decompiler/IL/Transforms/NullPropagationTransform.cs

@@ -272,7 +272,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 
 		static bool IsGetter(IMethod method)
 		{
-			return method.AccessorOwner is IProperty p && p.Getter == method;
+			return method.AccessorKind == System.Reflection.MethodSemanticsAttributes.Getter;
 		}
 
 		private void IntroduceUnwrap(ILVariable testedVar, ILInstruction varLoad, Mode mode)