Description of problem:
After user adds a subform in the Form Modeler, the server log gets the following message for each action done in the FM, until the default forms are set for the subform:

WARN  [org.jbpm.formModeler.panels.modeler.backend.EditionFormFinder] (...) Error getting form null from context formRenderCtx_1904520124_1450343389094: java.lang.IllegalArgumentException: Parameter named 'other' should be not null!

Simply adding the default form to the subform element stops these WARN logs.

The issue is two-fold. First, the log message doesn't really say much - anyone going through the logs won't have much of a clue what's wrong. Second, it really isn't a problem as long as the user just works on the form, all is good until the form is saved and used in such an invalid state. So the WARN msg is a bit unwarranted at this point.


Version-Release number of selected component (if applicable):
BPMS 6.2 CR2


Steps to Reproduce:
1. Create 2 forms with the Form Modeler, 'form' and 'subform'. Watch the server log.
2. Switch to 'Add fields by type' tab in the 'form'.
3. Add a 'Short text' element - nothing interesting in the server log.
4. Add 'Simple subform' element - server log shows the WARN msg.
5. Add a 'Short text' element - server log shows another WARN msg.
6. Edit the subform element - server log shows another WARN msg. But also the subform is automatically selected as the default (sub)form.
7. Add a 'Short text' element - no more WARNs in the server log.