Errors are not being propagated to UI on Create branch screen

When trying to use the "Create branch" link from a JIRA issue users are not shown any error message in the UI if the operation fails.

In this case, I was trying to create the branch "bugfix/3.6-FECRU-123-foo" however a branch simply called "bugfix" existed in the repo already. This meant that my branch could not be created.

Feedback in the UI is needed for any failed operation such as this.
In this case, the error message could be:

"Unable to create branch named "bugfix/foo" because a branch named "bugfix" already exists in this repository. Either select a different branch name prefix, or remove the 'bugfix' branch to continue."