{AH} return None in get_forward_sequence if sequence not defined, fixes #658
{AH} return None in get_forward_sequence if sequence not defined, fixes #658

kyleabeauchamp/pysam,pysam-developers/pysam,kyleabeauchamp/pysam,pysam-developers/pysam,kyleabeauchamp/pysam,pysam-developers/pysam,pysam-developers/pysam,kyleabeauchamp/pysam,kyleabeauchamp/pysam