Fixed a crash when metadata keys had no value
Fixed a crash when metadata keys had no value

RashmiNalwad/tika-similarity,harsham05/tika-similarity,YongchaoShang/tika-img-similarity,chrismattmann/tika-img-similarity,chrismattmann/tika-similarity,RashmiNalwad/tika-similarity,chrismattmann/tika-similarity,chrismattmann/tika-img-similarity,harsham05/tika-similarity,YongchaoShang/tika-img-similarity