rqt_graph show problem

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I encountered a problem when I used

rosrun rqt_graph rqt_graph

It showed:

PluginHandlerDirect._restore_settings() plugin "rqt_graph/RosGraph#0" raised an exception:
Traceback (most recent call last):
  File "/opt/ros/hydro/lib/python2.7/dist-packages/qt_gui/plugin_handler_direct.py", line 116, in _restore_settings
    self._plugin.restore_settings(plugin_settings_plugin, instance_settings_plugin)
  File "/opt/ros/hydro/lib/python2.7/dist-packages/rqt_graph/ros_graph.py", line 202, in restore_settings
    self._refresh_rosgraph()
  File "/opt/ros/hydro/lib/python2.7/dist-packages/rqt_graph/ros_graph.py", line 226, in _refresh_rosgraph
    self._update_graph_view(self._generate_dotcode())
  File "/opt/ros/hydro/lib/python2.7/dist-packages/rqt_graph/ros_graph.py", line 253, in _generate_dotcode
    quiet=quiet)
  File "/opt/ros/hydro/lib/python2.7/dist-packages/rqt_graph/dotcode.py", line 568, in generate_dotcode
    dotcode = dotcode_factory.create_dot(dotgraph)
  File "/opt/ros/hydro/lib/python2.7/dist-packages/qt_dotgraph/pydotfactory.py", line 160, in create_dot
    dot = graph.create_dot()
  File "/usr/lib/pymodules/python2.7/pydot.py", line 1595, in <lambda>
    lambda f=frmt, prog=self.prog : self.create(format=f, prog=prog))
  File "/usr/lib/pymodules/python2.7/pydot.py", line 1796, in create
    status, stderr_output) )
InvocationException: Program terminated with status: 1. stderr follows: Error: /tmp/tmpY9wRli:8: syntax error near line 8
context:  >>> label=NODE <<< ;

Could anyone figure out the reason? Thanks in advance!