Description of problem:
If a definition of WID does not contain the "icon" parameter then loading of Designer ends with this error in server.log:

15:50:48,667 ERROR [org.jbpm.designer.web.preprocessing.impl.JbpmPreprocessingUnit] (http-localhost/127.0.0.1:8080-2) Unable to parse a workitem definition: null

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

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

Actual results:
Object Library does not contains this custom task. Validation (step 3) was successful.

Expected results:
Use the default icon in Designer. The guided decision table editor does not require an icon in WID.