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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_flow_node_to_diagram(self, process_id, node_type, name, node_id=None):
 """ Helper function that adds a new Flow Node to diagram. It is used to add a new node of specified type. Adds a basic information inherited from Flow Node type. :param process_id: string object. ID of parent process, :param node_type: string object. Represents type of BPMN node passed to method, :param name: string object. Name of the node, :param node_id: string object. ID of node. Default value - None. """

        if node_id is None:
            node_id = BpmnDiagramGraph.id_prefix + str(uuid.uuid4())
        self.diagram_graph.add_node(node_id)
        self.diagram_graph.node[node_id][consts.Consts.id] = node_id
        self.diagram_graph.node[node_id][consts.Consts.type] = node_type
        self.diagram_graph.node[node_id][consts.Consts.node_name] = name
        self.diagram_graph.node[node_id][consts.Consts.incoming_flow] = []
        self.diagram_graph.node[node_id][consts.Consts.outgoing_flow] = []
        self.diagram_graph.node[node_id][consts.Consts.process] = process_id

        # Adding some dummy constant values
        self.diagram_graph.node[node_id][consts.Consts.width] = "100"
        self.diagram_graph.node[node_id][consts.Consts.height] = "100"
        self.diagram_graph.node[node_id][consts.Consts.x] = "100"
        self.diagram_graph.node[node_id][consts.Consts.y] = "100"
        return node_id, self.diagram_graph.node[node_id]