na_mask = NArray.int(record[:SEQ].length) unless na_mask
na_seq = NArray.to_na(record[:SEQ], "byte")
na_mask += na_seq.eq('-'.ord)
na_mask = NArray.int(record[:SEQ].length) unless na_mask
na_seq = NArray.to_na(record[:SEQ], "byte")
na_mask += na_seq.eq('-'.ord)