code: def _discarded_reads2_out_file_name(self):
          
          if self.Parameters['-4'].isOn():
              discarded_reads2 = self._absolute(str(self.Parameters['-4'].Value))
          else:
              raise ValueError(
                  "No discarded-reads2 (flag -4) output path specified")
          return discarded_reads2
docs: Checks if file name is set for discarded reads2 output.
             Returns absolute path.