Michele Morgan has requested that we look at these related bugs:
Note: The working branch for 1821950 adds an org unit setting to optionally allow blank call number labels, but needs work.
This issue is preventing some libraries from moving to the Angular editor.
New branch submitted that aims to resolve both Angular and AngularJS issues (needs testing):
https://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/user/mccanna/lp1980409_allow_empty_call_number_label