code: def import_activity_to_graph(diagram_graph, process_id, process_attributes, element):
          
          BpmnDiagramGraphImport.import_flow_node_to_graph(diagram_graph, process_id, process_attributes, element)
  
          element_id = element.getAttribute(consts.Consts.id)
          diagram_graph.node[element_id][consts.Consts.default] = element.getAttribute(consts.Consts.default) \
              if element.hasAttribute(consts.Consts.default) else None
docs: Method that adds the new element that represents BPMN activity.
          Should not be used directly, only as a part of method, that imports an element which extends Activity element
          (task, subprocess etc.)
  
          :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 element which extends 'activity'.