add_urls() raises BuildError during calling url_for()

[dahlia]

Some endpoints needs arguments (for example, delete_feed requires feed_id), so it raises werkzeug.routing.BuildError where these arguments are not given e.g. listing a category.

Traceback (most recent call last):
  File "/home/.../.local/lib/python3.4/site-packages/flask/app.py", line 1836, in __call__
    return self.wsgi_app(environ, start_response)
  ...
  File "/home/earthreader/.local/lib/python3.4/site-packages/flask/app.py", line 1461, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/earthreader/web/earthreader/web/__init__.py", line 184, in feeds
    add_urls(data, url_keys, cursor.category_id, child.feed_id)
  File "/home/earthreader/web/earthreader/web/__init__.py", line 117, in add_urls
    _external=True
  File "/home/earthreader/.local/lib/python3.4/site-packages/flask/helpers.py", line 312, in url_for
    return appctx.app.handle_url_build_error(error, endpoint, values)
  File "/home/earthreader/.local/lib/python3.4/site-packages/flask/app.py", line 1641, in handle_url_build_error
    reraise(exc_type, exc_value, tb)
  File "/home/earthreader/.local/lib/python3.4/site-packages/flask/_compat.py", line 33, in reraise
    raise value
  File "/home/earthreader/.local/lib/python3.4/site-packages/flask/helpers.py", line 305, in url_for
    force_external=external)
  File "/home/earthreader/.local/lib/python3.4/site-packages/werkzeug/routing.py", line 1616, in build
    raise BuildError(endpoint, values, method)
werkzeug.routing.BuildError: ('delete_feed', {}, None)