Empty RadioButtonGroups are invisible in the Web page designer

The Web page visual designer shows nothing at all when a RadioButtonGroup has no rows: the empty group occupies its layout slot but is invisible, so it is easy to miss or lose on the surface. The desktop visual designer shows a muted, non-interactive radio-button row labelled with the control type name for the same situation. Both designers should keep an empty RadioButtonGroup visible with the same muted facsimile.