[CAM-7580] Can't claim a task after the assignee was removed manually

Problem description:

given:
- I claim the user task in tasklist
- Remove the assignee of the task in cockpit by editing it manually
when:
- I claim the task again in tasklist
then:
- I get an error that the task is already claimed with the following message: An error happend while claiming the task. :
  Task '52908e8a-0a31-11e7-b08f-024213c7a31e' is already claimed by someone else.

Hints:
Checking the act_hi_op_log table shows that the deletion of the assignee leads to setting the assignee to "" instead of null.

Thorben Lindhauer added a comment - 06/Apr/17 9:37 AM Is this the same thing? https://app.camunda.com/jira/browse/CAM-3663

Johannes added a comment - 06/Apr/17 9:42 AM - edited

Likely yes, though it is a bit weird that the other ticket proclaims this issue as a feature

Johannes added a comment - 06/Apr/17 9:42 AM - edited Likely yes, though it is a bit weird that the other ticket proclaims this issue as a feature

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