rqt_tf_tree error

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Hi, I have installed the rqt_tf_tree. while running the command rosrun rqt_tf_tree rqt_tf_tree and getting the following terminal.

PluginHandlerDirect._restore_settings() plugin "rqt_tf_tree/RosTfTree#0" raised an exception:
Traceback (most recent call last):
  File "/opt/ros/indigo/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/indigo/lib/python2.7/dist-packages/rqt_tf_tree/tf_tree.py", line 129, in restore_settings
    self._refresh_tf_graph()
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rqt_tf_tree/tf_tree.py", line 138, in _refresh_tf_graph
    self._update_graph_view(self._generate_dotcode())
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rqt_tf_tree/tf_tree.py", line 147, in _generate_dotcode
    force_refresh=force_refresh)
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rqt_tf_tree/dotcode_tf.py", line 97, in generate_dotcode
    self.graph = self.generate(data, timer.now().to_sec())
  File "/opt/ros/indigo/lib/python2.7/dist-packages/rqt_tf_tree/dotcode_tf.py", line 137, in generate
    root,
UnboundLocalError: local variable 'root' referenced before assignment

I run with superuser also but the same error. can anybody help?