NullpointerException when removing from a role a group with an underscore in its name

[fbourasse]

Environment and versions used

Jahia 8.2.2.0

Steps to reproduce

• Install Jahia 8.2.2.0
• Create a group named test_jahia
• Add it to the role System administrator
• Try removing it with the red trash button ==> A NullPointerException will occur and the group won't be removed from the role

Current Behavior

Impossibility to remove from a role a group with a underscore

Desired Behavior

Possibility to remove from a role a group with a underscore

[fbourasse]

Here is the pull request: #127