Add class to post_class

I am looking to write a function that detects if a feature image has been added to a post, and to add a class if it has. I have written this so far.

// Add a class to post_class if feature image is detected
function check_image( $class ) {
	if ( has_post_thumbnail() ) {
		$class[] = 'feature-image';
	}
	return $class;
	}
add_filter('post_class', 'check_image');
// end ---

This actually works but I am getting an error “Missing argument 1 for check_image()”. Any ideas?? I am quite new to writing WordPress functions so go easy ??