code: def _unassembled_reads1_out_file_name(self):
          
          if self.Parameters['-1'].isOn():
              unassembled_reads1 = self._absolute(
                  str(self.Parameters['-1'].Value))
          else:
              raise ValueError("No reads1 (flag: -1) output path specified")
          return unassembled_reads1
docs: Checks file name is set for reads1 output.
             Returns absolute path.