Using URLDecoder instead of String.replaceAll

See https://github.com/fcrepo4/fcrepo4/commit/494ab59e9c3a14794aebbb1bfe7c4700e076d49d#commitcomment-7172975
Why is there a NPE catch clause? I do not believe "subjects" nor "subject" will ever be null at this point, and I am not seeing an NPE defined on the decode() method.