TypeError: cannot return std::string from Unicode object

[jyder4@…]

Error was occured when I click one of the milestone from table of milestone at dashboard.

How to Reproduce

While doing a GET operation on /mdashboard/4.3.1.3, Trac issued an internal error.

(please provide additional details here)

Request parameters:

{'id': u'4.3.1.3', 'imagename': None}

System Information

Trac	0.11dev-r6425
Python	2.5.1 (r251:54863, Apr 18 2007, 08:51:08) [MSC v.1310 32 bit (Intel)]
setuptools	0.6c7
SQLite	3.5.2
pysqlite	2.4.0
Genshi	0.5dev-r789
mod_python	3.3.1
Pygments	0.9
Subversion	1.4.6 (r28521)

Python Traceback

Traceback (most recent call last):
  File "g:\python25\lib\site-packages\Trac-0.11dev_r6425-py2.5.egg\trac\web\main.py", line 406, in _dispatch_request
    dispatcher.dispatch(req)
  File "g:\python25\lib\site-packages\Trac-0.11dev_r6425-py2.5.egg\trac\web\main.py", line 195, in dispatch
    resp = chosen_handler.process_request(req)
  File "build\bdist.win32\egg\tracmetrixplugin\mdashboard.py", line 431, in process_request
    return self._render_view(req, db, milestone)
  File "build\bdist.win32\egg\tracmetrixplugin\mdashboard.py", line 557, in _render_view
    create_cumulative_chart(self.env, milestone, numdates, tkt_cumulative_table)
  File "build\bdist.win32\egg\tracmetrixplugin\mdashboard.py", line 324, in create_cumulative_chart
    fig.savefig(path)
  File "G:\Python25\Lib\site-packages\matplotlib\figure.py", line 782, in savefig
    self.canvas.print_figure(*args, **kwargs)
  File "G:\Python25\Lib\site-packages\matplotlib\backend_bases.py", line 1195, in print_figure
    **kwargs)
  File "G:\Python25\Lib\site-packages\matplotlib\backends\backend_agg.py", line 397, in print_png
    self.get_renderer()._renderer.write_png(filename, self.figure.dpi.get())
TypeError: cannot return std::string from Unicode object