Werkzeug Internal Server Error

traceback.txt

Traceback (most recent call last):
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/flask/app.py", line 1836, in __call__
    return self.wsgi_app(environ, start_response)
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/flask/app.py", line 1820, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/flask/app.py", line 1403, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/flask/_compat.py", line 33, in reraise
    raise value
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/flask/app.py", line 1817, in wsgi_app
    response = self.full_dispatch_request()
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/flask/app.py", line 1477, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/flask/app.py", line 1381, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/flask/_compat.py", line 33, in reraise
    raise value
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/flask/app.py", line 1475, in full_dispatch_request
    rv = self.dispatch_request()
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/flask/app.py", line 1461, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/Users/chenwang/Documents/python/Flask Social/app.py", line 52, in register
    return render_template('register.html', form=form)
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/flask/templating.py", line 128, in render_template
    context, ctx.app)
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/flask/templating.py", line 110, in _render
    rv = template.render(context)
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/jinja2/environment.py", line 969, in render
    return self.environment.handle_exception(exc_info, True)
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/jinja2/environment.py", line 742, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/jinja2/_compat.py", line 36, in reraise
    raise value.with_traceback(tb)
  File "/Users/chenwang/Documents/python/Flask Social/templates/register.html", line 2, in <module>
    {% from 'macros.html' import render_field %}
  File "/Users/chenwang/Documents/python/Flask Social/templates/layout.html", line 71, in <module>
    <a href="{{ url_for('stream', username=current_user.username) }}">Following</a>
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/flask/helpers.py", line 312, in url_for
    return appctx.app.handle_url_build_error(error, endpoint, values)
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/flask/app.py", line 1641, in handle_url_build_error
    reraise(exc_type, exc_value, tb)
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/flask/_compat.py", line 33, in reraise
    raise value
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/flask/helpers.py", line 305, in url_for
    force_external=external)
  File "/Users/chenwang/pythonenv/social/lib/python3.4/site-packages/werkzeug/routing.py", line 1678, in build
    raise BuildError(endpoint, values, method)
werkzeug.routing.BuildError: ('stream', {'username': 'Chen Wang'}, None)