Comment (by Roland Haas):

Sorry I did not want to claim that it is exactly a line that looks like that or that the variable is named CONFIGS_DIR, just that errors like this (trying to access a file in "/") are usually caused by this type of issue. Note that I cannot reproduce this using the current candidate for the Proca release.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/2236/formaline-fails-for-trying-to-remove-non