fix bug in transforming empty strings in scan key
fix bug in transforming empty strings in scan key

omegaga/peloton,larryxiao/peloton,larryxiao/peloton,larryxiao/peloton,amaliujia/CMUDB-peloton,larryxiao/peloton-1,larryxiao/peloton,ranxian/peloton,omegaga/peloton,omegaga/peloton,larryxiao/peloton,larryxiao/peloton-1,omegaga/peloton,larryxiao/peloton-1,amaliujia/CMUDB-peloton,ranxian/peloton,larryxiao/peloton-1,omegaga/peloton,amaliujia/CMUDB-peloton,larryxiao/peloton,omegaga/peloton,larryxiao/peloton-1,larryxiao/peloton-1,amaliujia/CMUDB-peloton,ranxian/peloton,ranxian/peloton,larryxiao/peloton,ranxian/peloton,ranxian/peloton,amaliujia/CMUDB-peloton,larryxiao/peloton-1,amaliujia/CMUDB-peloton,omegaga/peloton,amaliujia/CMUDB-peloton