# 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.
LOG.debug('Lambda archive content:\n%s' % file_list)
                raise ClientError(error_response(
                    'Unable to find handler script in Lambda archive. %s' % config_debug,
                    400, error_type='ValidationError'))
        if runtime.startswith('python') and not use_docker():
            try:
                
                ensure_readable(main_file)
                zip_file_content = load_file(main_file, mode='rb')
                
                lambda_handler = exec_lambda_code(
                    zip_file_content,
                    handler_function=handler_function,
                    lambda_cwd=lambda_cwd,
                    lambda_env=lambda_environment)
            except Exception as e:
                raise ClientError('Unable to get handler function from lambda code.', e)
    add_function_mapping(lambda_name, lambda_handler, lambda_cwd)
    return {'FunctionName': lambda_name}
def do_list_functions():
    funcs = []
    for f_arn, func in arn_to_lambda.items():
        if type(func) != LambdaFunction:
            continue
        func_name = f_arn.split(':function:')[-1]
        arn = func_arn(func_name)
        func_details = arn_to_lambda.get(arn)
        funcs.append(format_func_details(func_details))
    return funcs
def format_func_details(func_details, version=None, always_add_version=False):