Description of problem:
I have tried to use the default WID definition which contains a new WID.
This definition contains the empty string for parameter "icon".

It cause this error in server log:
15:20:17,670 ERROR [org.jbpm.designer.web.preprocessing.impl.JbpmPreprocessingUnit] (http-localhost/127.0.0.1:8080-4) Unable to parse a workitem definition: String index out of range: -1

It says nothing about the problem. The validation is ok and the new custom task is not present in Object Library of Designer. The ordinary user does not know what happens.

Version-Release number of selected component (if applicable):
6.0.2 ER2 BPMS

How reproducible:

Steps to Reproduce:
1. create new WID
2. validate it and save it
3. create new process in the same package

Actual results:
Object Library does not contains this custom task. Validation (step 2) was successful.

Expected results:
Option1:

• validation fails and it shows message like "The empty string is not allowed for the 'icon' parameter in definition ${taskname}".
  Option2:
• if the "icon" parameter is empty, use default icon.

Additional info: