# Steps to reproduce

* Start `localstack` (version 0.10.3).
* Don't create any lambda functions.
* Run:

```sh
AWS_ACCESS_KEY_ID='a' AWS_SECRET_ACCESS_KEY='b' \
aws lambda invoke \
  --function-name 'my-func' \
  --qualifier='qual' \
  --endpoint http://localhost:4574 test.out
```

* Expected behaviour — a `ResourceNotFoundException` from `aws-cli`.
* Actual behaviour — `An error occurred (500) when calling the Invoke operation` message and a 500 response.

This bug only appears if a `qualifier` is included in the request.
""" List functions
        ---
        operationId: 'listFunctions'
        parameters:
            - name: 'request'
              in: body
    """
    funcs = do_list_functions()
    result = {}
    result['Functions'] = funcs
    return jsonify(result)
@app.route('%s/functions/<function>' % PATH_ROOT, methods=['DELETE'])
def delete_function(function):
    """ Delete an existing function
        ---
        operationId: 'deleteFunction'
        parameters:
            - name: 'request'
              in: body