Exception when using POST

Example:

ERROR:flask.app:Exception on /api/ [POST]
Traceback (most recent call last):
  File "/usr/local/lib/python3.5/site-packages/flask/app.py", line 2292, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python3.5/site-packages/flask/app.py", line 1815, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/local/lib/python3.5/site-packages/flask/app.py", line 1718, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/local/lib/python3.5/site-packages/flask/_compat.py", line 35, in reraise
    raise value
  File "/usr/local/lib/python3.5/site-packages/flask/app.py", line 1813, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/local/lib/python3.5/site-packages/flask/app.py", line 1799, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/usr/src/app/senpy/blueprints.py", line 177, in decorated_function
    prefix=params.get('prefix', encoded_url()),
  File "/usr/src/app/senpy/blueprints.py", line 72, in encoded_url
    hash(frozenset(request.form.params().items()))
AttributeError: 'ImmutableMultiDict' object has no attribute 'params'