EPM Automate error trapping for importBalances command

Summary:

I am developing EPM Automate scripts via Groovy and have run into an issue with error trapping for the importBalances command. If the import is "successful", but there are invalid mappings, it still results in a status of "0". See the code I am using in the Code Snippet section below for how I am looking for errors. Below is the output from the EPM Automate importBalances command (it is run from FCC)

My question is: what is the best way to look for that Invalid Mapping warning? Is there a way to check to see if the output contains "Warning"? I tried specifying the full output (starting with "importBalances completed successfully"), but I cannot seem to get it to match the output to generate an error for the rule.