code: def set_doc_data_lics(self, doc, lics):
          
          if not self.doc_data_lics_set:
              self.doc_data_lics_set = True
              if validations.validate_data_lics(lics):
                  doc.data_license = document.License.from_identifier(lics)
                  return True
              else:
                  raise SPDXValueError('Document::DataLicense')
          else:
              raise CardinalityError('Document::DataLicense')
docs: Sets the document data license.
          Raises value error if malformed value, CardinalityError
          if already defined.