code: def import_parallel_gateway_to_graph(diagram_graph, process_id, process_attributes, element):
          
          BpmnDiagramGraphImport.import_gateway_to_graph(diagram_graph, process_id, process_attributes, element)
docs: Adds to graph the new element that represents BPMN parallel gateway.
          Parallel gateway doesn't have additional attributes. Separate method is used to improve code readability.
  
          :param diagram_graph: NetworkX graph representing a BPMN process diagram,
          :param process_id: string object, representing an ID of process element,
          :param process_attributes: dictionary that holds attribute values of 'process' element, which is parent of
              imported flow node,
          :param element: object representing a BPMN XML 'parallelGateway'.