Description of problem:

The Refresh button on my Dynamic Dropdown Lists runs the method which uses "nil" as hash key cause UI to hang with
the waiting wheel.


Version-Release number of selected component (if applicable):
 5.4.1.0.20150717083323_6ed7e1c 

How reproducible:
Always

Steps to Reproduce:

1. Create a custom dialog with a Dynamic Dropdown List and a Refresh button
2. Create a method that is call when hiting refresh, use "nil" as hash key the method
3. Call the dialog from a service provisioning or custom button
4. Click on "Refresh"

Actual results:
The UI hangs.


Expected results:
The UI is refreshed with the "dialog_field" generate in the method.

Additional info:
Using an empty string instead of nil as hash key solves the problem, this bugzila is  opened to support "nil" .