Add 0/null checks for various cases in the COM/dynamic VARIANT extensions

src/libraries/Common/src/System/Runtime/InteropServices/BuiltInVariantExtensions.cs

@@ -21,7 +21,7 @@ private static unsafe ref T GetByRefDataRef<T>(this ref ComVariant variant)
             return ref Unsafe.AsRef<T>((void*)variant.GetRawDataRef<nint>());
         }
 
-        public static unsafe void CopyFromIndirect(this ref ComVariant variant, object value)
+        public static unsafe void CopyFromIndirect(this ref ComVariant variant, object? value)
         {
             VarEnum vt = (VarEnum)(((int)variant.VarType) & ~((int)VarEnum.VT_BYREF));
 
@@ -154,9 +154,8 @@ public static unsafe void CopyFromIndirect(this ref ComVariant variant, object v
                 VarEnum.VT_DECIMAL => variant.As<decimal>(),
                 VarEnum.VT_CY => decimal.FromOACurrency(variant.GetRawDataRef<long>()),
                 VarEnum.VT_DATE => variant.As<DateTime>(),
-                VarEnum.VT_BSTR => Marshal.PtrToStringBSTR(variant.GetRawDataRef<nint>()),
-                VarEnum.VT_UNKNOWN => Marshal.GetObjectForIUnknown(variant.GetRawDataRef<nint>()),
-                VarEnum.VT_DISPATCH => Marshal.GetObjectForIUnknown(variant.GetRawDataRef<nint>()),
+                VarEnum.VT_BSTR => variant.GetRawDataRef<nint>() is 0 ? null : Marshal.PtrToStringBSTR(variant.GetRawDataRef<nint>()),
+                VarEnum.VT_UNKNOWN or VarEnum.VT_DISPATCH => variant.GetRawDataRef<nint>() is 0 ? null : Marshal.GetObjectForIUnknown(variant.GetRawDataRef<nint>()),
                 _ => GetObjectFromNativeVariant(ref variant),
             };
         }

src/libraries/Microsoft.CSharp/src/Microsoft/CSharp/RuntimeBinder/ComInterop/DynamicVariantExtensions.cs

@@ -379,14 +379,14 @@ public static void SetBstr(this ref ComVariant variant, string value)
             variant = ComVariant.Create(new BStrWrapper(value));
         }
 
-        public static void SetUnknown(this ref ComVariant variant, object value)
+        public static void SetUnknown(this ref ComVariant variant, object? value)
         {
-            variant = ComVariant.CreateRaw(VarEnum.VT_UNKNOWN, Marshal.GetIUnknownForObject(value));
+            variant = ComVariant.CreateRaw(VarEnum.VT_UNKNOWN, value is null ? IntPtr.Zero : Marshal.GetIUnknownForObject(value));
         }
 
-        public static void SetDispatch(this ref ComVariant variant, object value)
+        public static void SetDispatch(this ref ComVariant variant, object? value)
         {
-            variant = ComVariant.CreateRaw(VarEnum.VT_DISPATCH, Marshal.GetIDispatchForObject(value));
+            variant = ComVariant.CreateRaw(VarEnum.VT_DISPATCH, value is null ? IntPtr.Zero : Marshal.GetIDispatchForObject(value));
         }
 
         public static void SetError(this ref ComVariant variant, int value)

src/tests/Interop/COM/Dynamic/BasicTest.cs

@@ -423,6 +423,9 @@ private void Null()
 
             obj.String_Property = null;
             Assert.Equal(string.Empty, obj.String_Property);
+
+            obj.Dispatch_Property = new DispatchWrapper(null);
+            Assert.Null(obj.Dispatch_Property);
         }
 
         private void StringWrapper(string toWrap, string expected)