In GenerateRequests.php::handleResponse()
Code does (currently line 294)
$response_models[] = "'$code_string' => '$type'";
Except $type has been set as one of:
$type = "\\$model_ns\\$type::class";
$type = "''";
Where the quotation marks are either not wanted, or already included.
I believe the fix should be simply to remove the ' from around $type in the line
$response_models[] = "'$code_string' => '$type'";
referred to above.