closes #514.

test added to tests/CSharpTemp/CSharpTemp.Tests.cs

src/Generator/Generators/CSharp/CSharpMarshal.cs

@@ -401,9 +401,8 @@ namespace CppSharp.Generators.CSharp
 
         public bool VisitDelegateType(FunctionType function, string type)
         {
-            Context.Return.Write("Marshal.GetFunctionPointerForDelegate({0})",
+            Context.Return.Write("{0} == null ? global::System.IntPtr.Zero : Marshal.GetFunctionPointerForDelegate({0})",
                   Context.Parameter.Name);
-
             return true;
         }
 

tests/CSharpTemp/CSharpTemp.Tests.cs

@@ -327,4 +327,14 @@ public class CSharpTempTests : GeneratorTestFixture
         dervClass = new TestParamToInterfacePass(dervClass + baseInterface);
         Assert.AreEqual(dervClass.M, 2);
     }
+
+    [Test]
+    public void TestNullAttributedFunctionPtr()
+    {
+        using (var foo = new Foo())
+        {
+            foo.AttributedFunctionPtr = null;
+        }
+    }
+
 }