docs: def _split_line(self, line_str):
          """Split line and check number of columns"""
          arr = line_str.rstrip().split("\t")
          if len(arr) != self.expected_fields:
              raise exceptions.InvalidRecordException(
                  (
                      "The line contains an invalid number of fields. Was "
                      "{} but expected {}\n{}".format(len(arr), 9 + len(self.samples.names), line_str)
                  )
              )
          return arr