What should happen if the file is not found? you use the string xslt here on this line - https://github.com/OpenMS/OpenMS/pull/707/files#diff-2c7f781f44f688dd4ba6750ff788b1b6R1079  what happens when an empty string is written instead? Please document the behaviour for a missing file properly and also handle the FileNotFound accordingly (at least write a warning such that the user knows what is not working)