use stricter/faster type for comparison

Author: kkmuffme

src/wp-includes/plugin.php

@@ -507,7 +507,7 @@ function do_action( $hook_name, ...$arg ) {
 		$wp_current_filter[] = $hook_name;
 	}
 
-	if ( empty( $arg ) ) {
+	if ( $arg === array() ) {
 		$arg[] = '';
 	}