Unable to create issue with unassigned value in assignee field

Steps to Reproduce:

1. Create a new Project (DEMO Project)
2. Create a new issue by clicking the "Create Issue" button on top.
3. Set the Asiggnee to Unassigned.
4. Click Create.

Expected Result:
The issue will be created.

Actual Result:

• The issue would not created.
• It will stays in the Create issue window with a NullPointerException.

Workaround:
Create the issue in a new tab (Middle click on the "Create Issue" button)