<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def export_start_event(bpmn_graph, export_elements, node, nodes_classification, order=0, prefix="", condition="", who=""):
 """ Start event export :param bpmn_graph: an instance of BpmnDiagramGraph class, :param export_elements: a dictionary object. The key is a node ID, value is a dictionary of parameters that will be used in exported CSV document, :param node: networkx.Node object, :param order: the order param of exported node, :param nodes_classification: dictionary of classification labels. Key - node id. Value - a list of labels, :param prefix: the prefix of exported node - if the task appears after some gateway, the prefix will identify the branch :param condition: the condition param of exported node, :param who: the condition param of exported node, :return: None or the next node object if the exported node was a gateway join. """


        # Assuming that there is only one event definition
        event_definitions = node[1].get(consts.Consts.event_definitions)
        if event_definitions is not None and len(event_definitions) > 0:
            event_definition = node[1][consts.Consts.event_definitions][0]
        else:
            event_definition = None

        if event_definition is None:
            activity = node[1][consts.Consts.node_name]
        elif event_definition[consts.Consts.definition_type] == "messageEventDefinition":
            activity = "message " + node[1][consts.Consts.node_name]
        elif event_definition[consts.Consts.definition_type] == "timerEventDefinition":
            activity = "timer " + node[1][consts.Consts.node_name]
        else:
            activity = node[1][consts.Consts.node_name]

        export_elements.append({"Order": prefix + str(order), "Activity": activity, "Condition": condition,
                                "Who": who, "Subprocess": "", "Terminated": ""})

        outgoing_flow_id = node[1][consts.Consts.outgoing_flow][0]
        outgoing_flow = bpmn_graph.get_flow_by_id(outgoing_flow_id)
        outgoing_node = bpmn_graph.get_node_by_id(outgoing_flow[2][consts.Consts.target_ref])
        return BpmnDiagramGraphCsvExport.export_node(bpmn_graph, export_elements, outgoing_node, nodes_classification,
                                                     order + 1, prefix, who)