Steps to reproduce

1. Click on Processes
2. Open the process definition runtime view by clicking on the name of a process with no job definitions (e. g. CallActivity)
3. Click on the right side on the button to change the overriding job priority of the process definition
4. A modal dialog is opened
5. Select either the "clear overriding job priority" radio button or the "set overriding job priority" radio button and set a priority
6. Click on "Clear"

Observed behavior

1. An empty table is shown
2. The modal dialog cannot be closed by clicking neither on the "Close" nor on the "Clear" button

Expected behavior

1. Error notification in dialog is shown