Your description doesn't make sense to me.
The expression you have given just returns some string, nothing else. It cannot "fail".
What do you mean?
Please be a bit more specific and explicit.
How are you expected to process this file?
What is the expected outcome?
Two small examples would help.
Sample expression you have given which returns the string and it wont fail. Unless abort function used in the expression.
Provide with some examples for understanding, so we can assist it better.