# System.Windows.Forms.Design

``` diff
 namespace System.Windows.Forms.Design {
     public class AxImporter {
         public interface IReferenceResolver {
-            string ResolveActiveXReference(UCOMITypeLib typeLib);
+            string? ResolveActiveXReference(UCOMITypeLib typeLib);
-            string ResolveComReference(AssemblyName name);
+            string? ResolveComReference(AssemblyName name);
-            string ResolveComReference(UCOMITypeLib typeLib);
+            string? ResolveComReference(UCOMITypeLib typeLib);
-            string ResolveManagedReference(string assemName);
+            string? ResolveManagedReference(string assemName);
         }
     }
     public class ControlDesigner : ComponentDesigner {
         public class ControlDesignerAccessibleObject : AccessibleObject {
-            public override string? Description { get; }
+            public override string Description { get; }
-            public override AccessibleObject? Parent { get; }
+            public override AccessibleObject Parent { get; }
-            public override string? Value { get; }
+            public override string Value { get; }
-            public override AccessibleObject? GetChild(int index);
+            public override AccessibleObject GetChild(int index);
-            public override AccessibleObject? GetFocused();
+            public override AccessibleObject GetFocused();
-            public override AccessibleObject? GetSelected();
+            public override AccessibleObject GetSelected();
-            public override AccessibleObject? HitTest(int x, int y);
+            public override AccessibleObject HitTest(int x, int y);
         }
     }
     public interface IWindowsFormsEditorService {
-        void DropDownControl(Control? control);
+        void DropDownControl(Control control);
     }
     public abstract class MaskDescriptor {
-        public static bool IsValidMaskDescriptor(MaskDescriptor maskDescriptor, out string validationErrorDescription);
+        public static bool IsValidMaskDescriptor(MaskDescriptor? maskDescriptor, out string validationErrorDescription);
     }
 }
```

