It seems like the symbol flymake--mode-line-format is no longer found in the flymake package's code, so this was raising a void symbol error. Quoting it should keep it backwards compatible for whatever behavior this was using previously, and prevent the error from making it so the flymake-mode-line-format variable was not being processed.
It seems like the symbol flymake--mode-line-format is no longer found in the flymake package's code, so this was raising a void symbol error. Quoting it should keep it backwards compatible for whatever behavior this was using previously, and prevent the error from making it so the flymake-mode-line-format variable was not being processed.