# 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.
""" Get an existing event source mapping
        ---
        operationId: 'getEventSourceMapping'
        parameters:
            - name: 'request'
              in: body
    """
    mappings = event_source_mappings
    mappings = [m for m in mappings if mapping_uuid == m.get('UUID')]
    if len(mappings) == 0:
        return not_found_error()
    return jsonify(mappings[0])
@app.route('%s/event-source-mappings/' % PATH_ROOT, methods=['POST'])
def create_event_source_mapping():