WooCommerce Name Your Price: Make NYP field required

functions

add_filter( 'woocommerce_add_to_cart_validation', 'woocommerce_nyp_make_field_required', 10, 5 );

function woocommerce_nyp_make_field_required( $passed, $product_id, $quantity, $variation_id = '', $variations= '' ) {

	if( $variation_id )
		$product_id = $variation_id;

	// skip if not a nyp product - send original status back
	if ( ! WC_Name_Your_Price_Helpers::is_nyp( $product_id ) ){
		return $passed;
	}

	$posted_nyp_field = 'nyp' . apply_filters( 'nyp_field_prefix', '', $product_id );

	$input = $_POST[ $posted_nyp_field ];

	// set a null string to 0
	if ( ! isset( $_POST[ $posted_nyp_field ] ) || empty( $_POST[ $posted_nyp_field ] ) ){
		$passed = false;
		wc_add_notice( 'You really need to enter something.', 'error' );
	}

	return $passed;

}