# 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 event source mappings
        ---
        operationId: 'listEventSourceMappings'
    """
    event_source_arn = request.args.get('EventSourceArn')
    function_name = request.args.get('FunctionName')
    mappings = event_source_mappings
    if event_source_arn:
        mappings = [m for m in mappings if event_source_arn == m.get('EventSourceArn')]
    if function_name:
        function_arn = func_arn(function_name)
        mappings = [m for m in mappings if function_arn == m.get('FunctionArn')]
    response = {
        'EventSourceMappings': mappings
    }
    return jsonify(response)
@app.route('%s/event-source-mappings/<mapping_uuid>' % PATH_ROOT, methods=['GET'])
def get_event_source_mapping(mapping_uuid):