def import_activity_to_graph(diagram_graph, process_id, process_attributes, element):
        """
        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'.
        """
        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