[regression] TextBox: possibility of "this.templateString is null" on custom dijit.form.TextBox extensions upgrading from 1.3 to 1.5

[Kenneth G. Franqueiro]

Developers upgrading from 1.3 to 1.4+ may experience an exception on any custom dojo.declared extensions of dijit.form.TextBox (or its subclasses such as ValidationTextBox), due to code that likely changed with the deprecation of templatePath.

If a custom class declared based on TextBox has overridden its templateString and set it to null (presumably to force templatePath to take precedence), an exception will occur due to TextBox's postMixInProperties method referencing templateString with the assumption it is defined.

An example is attached; it might be easier to understand from there.

Obviously this can be solved if the developer simply brings their custom component up to date with the 1.4+ paradigm of using templateString together with dojo.cache, so this bug is likely low in priority; however, out of the box it will cause such customizations to break, which is undesirable - templatePath is currently deprecated but not unsupported.

[Kenneth G. Franqueiro]

test to reproduce issue (run against a source distribution of dojo, revise path to dojo.js as necessary)

[Douglas Hays]

Not a problem in 1.4.

[Douglas Hays]

(In [22608]) References #11493 (trunk/1.6). Check for non-null templateString before accessing and add simple test for null to test_validate.html

[Douglas Hays]

(In [22609]) Fixes #11493. Backport [22608] to 1.5.1.