null values on TextBox widget 'value' property cause display error.

[csawyer@…]

var mnameWdgt = dojo.widget.createWidget('textbox',{id:'mname',value:middle_name});

if middle_name is null (the javascript null) then the widget will display:

${this.value}

as the value in the box. I'm not sure what the 'right' behavior is (show nothing or show 'null').

Personally I'd vote for 'show nothing'

[Douglas Hays]

(In [7526]) Fixes #1651. Testcase added to tests/form/test_validate.html