WordPress: custom function to redirect posts if a specific meta field is empty

In this example, I have a custom post type called "partner". When the meta field "header_2" is empty, the post single should not be active, which is why I want it to post to 404. I wrote a custom function that redirects to 404 if the field is empty.

add_action( 'template_redirect', 'redirct_if_empty' );
function redirct_if_empty() {
	if (!is_singular( 'partner') ) {return false;}
	global $post;
	$field = get_post_meta( $post->ID, 'header_2', true );
	if ( empty( $field ) ) {
		header("HTTP/1.1 404 Not Found");
		header("Location:" . get_template_part( 404 )); /* Redirect browser */
		exit();
	}
}

How do I check my website's status code?
You can use DevTools in Google Chrome (F12 + "Network" tab) and the first element should be your website's status code at type "document"