Regression in content_rating_mapper to map rating to none

[burkasaurusrex]

Version Number

1.18.0

What branch are you on?

master

Describe the Bug

content_rating_mapper appears to work except for when I map a rating to an empty rating. For the movies where it should be removed, there is an extra log line that says No Content Rating Found. I should note that I've tried it with and without double quotes around the mapped rating.

Relevant Collection/Overlay/Playlist Definition

operations:
      content_rating_mapper:
        "TV-G": G
        "TV-PG": PG
        "TV-14": PG-13
        "TV-MA": R
        Approved: PG
        Passed: PG
        NR: 
        "Not Rated": 
        Unrated:

Logs

https://gist.github.com/burkasaurusrex/0754a8e6f69fd2119beedfe4b38ae6da