When I call diffFilter on an empty change set, it logs a "No lines found!" error but returns a 0 success code.

For example:

diffFilter --phpcsStrict < (git diff HEAD...HEAD)  phpcs.json --report=phpcs 0

outputs an empty string, instead of a JSON object.

In my scripting, when a command returns success code, I assume it produced the output in expected format as it does for any successful input and run.
If the command encounters an error, making it unable to proceed to produce meaningful output, it should return error code, so I could catch that and act accordingly.

But, the line

• log a successful JSON response - if there are no lines, there are no phpCS errors as well. Consider no lines a valid input, #73
• return error code - if it's unable to produce a meaningful, compliant result, if it got invalid arguments, it should fail in an observable manner. Return error exit code for "No lines…" error. #74