Creating Label layer fails (keyError: line 531) when creating after join on base layer

[jatkins23]

In looping through the sourceFeature and labelFeature attributes (lines 529 - 531), the program fails with an uncaught KeyError when operating on a table with joined in data. I believe it searches for columns in the join that are not present in the newly created label layer but I am not sure.

Work-around!
I have found a solution by creating the label layer before joining and then joining the same csv to both layers (since my symbology and labels are dependent on the joined data), however, it would be ideal to not have to join this twice or at least to have the error caught or since it was pretty difficult to diagnose.