CommitValidationMessages are transformed to "Code Review Error - 500 Internal server error" in frontend

[GoogleCodeExporter]

Affected Version: Gerrit Code Review 2.11.1

What steps will reproduce the problem?
1. create a class that implements CommitValidationListener
2. fill the returning CommitValidationMessage List with errors
3. change the commit message with new online editing tools
4. click on publish changes

What is the expected output? What do you see instead?
* Expected: A warning/error that the commit message is invalid and the 
warning/error text
* Actual: _Blackscreen_ only with "Code Review Error - 500 Internal server 
error"

Please provide any additional information below.

[2015-06-21 14:55:07,247] ERROR com.google.gerrit.httpd.restapi.RestApiServlet 
: Error in POST /changes/81274/edit:publish
com.google.gerrit.server.project.InvalidChangeOperationException: Commit 
Message Problem: please add more details about [...]

Original issue reported on code.google.com by stock...@gmail.com on 21 Jun 2015 at 1:15

[GoogleCodeExporter]

https://gerrit-review.googlesource.com/#/c/68842/

Original comment by david.pu...@sonymobile.com on 22 Jun 2015 at 8:23

• Changed state: ChangeUnderReview

[GoogleCodeExporter]

Original comment by edwin.ke...@gmail.com on 23 Jun 2015 at 9:16

• Changed state: Submitted
• Added labels: FixedIn-2.12