code: def write_modulators_to_project_file(self, tree=None):
          
          if self.project_file is None or not self.modulators:
              return
  
          if tree is None:
              tree = ET.parse(self.project_file)
  
          root = tree.getroot()
          root.append(Modulator.modulators_to_xml_tag(self.modulators))
  
          tree.write(self.project_file)
docs: :type modulators: list of Modulator
          :return: