Get error when View Design a class file which contains a var

I add one line to my class:
DEFINE VARIABLE integerList AS "List<INTEGER>" NO-UNDO.

It compiles and check syntax ok, but when View Design, get error
"Visual Designer cannot load this class, line 24: unable to resolve type information for type List<System.Int32> for field integerList"

How to fix it?

Here is code:

BLOCK-LEVEL ON ERROR UNDO, THROW.

USING "System.Collections.Generic.List<INTEGER>" FROM ASSEMBLY.
USING Progress.Windows.Form FROM ASSEMBLY.

CLASS Test INHERITS Form:

    DEFINE PRIVATE VARIABLE components AS System.ComponentModel.IContainer NO-UNDO.
    
    DEFINE VARIABLE integerList AS "List<INTEGER>" NO-UNDO.

    CONSTRUCTOR PUBLIC Test (  ):

        SUPER().
     
        InitializeComponent().
        THIS-OBJECT:ComponentsCollection:ADD(THIS-OBJECT:components).
   
        CATCH e AS Progress.Lang.Error:
            UNDO, THROW e.
        END CATCH.

    END CONSTRUCTOR.


    METHOD PRIVATE VOID InitializeComponent(  ):

        /* NOTE: The following method is automatically generated.

        We strongly suggest that the contents of this method only be modified using the
        Visual Designer to avoid any incompatible modifications.

        Modifying the contents of this method using a code editor will invalidate any support for this file. */
        THIS-OBJECT:SuspendLayout().
        /*  */
        /* Test */
        /*  */
        THIS-OBJECT:ClientSize = NEW System.Drawing.Size(292, 266).
        THIS-OBJECT:Name = "Test":U.
        THIS-OBJECT:Text = "Test":U.
        THIS-OBJECT:ResumeLayout(FALSE).
        CATCH e AS Progress.Lang.Error:
            UNDO, THROW e.
        END CATCH.
    END METHOD.

    DESTRUCTOR PUBLIC Test ( ):

    END DESTRUCTOR.

END CLASS.