Code Quality: Explicitly return null when documented instead of void.

This fixes a PHPStan rule level 3 error: `return.empty`.

Developed in #10995

Props huzaifaalmesbah, westonruter, shailu25, mukesh27, noruzzaman.
See #64238.


git-svn-id: https://develop.svn.wordpress.org/trunk@61716 602fd350-edb4-49c9-b593-d223f7449a82

Author: westonruter

src/wp-admin/includes/file.php

@@ -2187,7 +2187,7 @@ function WP_Filesystem( $args = false, $context = false, $allow_relaxed_file_own
 		$abstraction_file = apply_filters( 'filesystem_method_file', ABSPATH . 'wp-admin/includes/class-wp-filesystem-' . $method . '.php', $method );
 
 		if ( ! file_exists( $abstraction_file ) ) {
-			return;
+			return null;
 		}
 
 		require_once $abstraction_file;

src/wp-admin/includes/plugin.php

@@ -926,7 +926,7 @@ function delete_plugins( $plugins, $deprecated = '' ) {
 			require_once ABSPATH . 'wp-admin/admin-footer.php';
 			exit;
 		}
-		return;
+		return null;
 	}
 
 	if ( ! WP_Filesystem( $credentials ) ) {
@@ -941,7 +941,7 @@ function delete_plugins( $plugins, $deprecated = '' ) {
 			require_once ABSPATH . 'wp-admin/admin-footer.php';
 			exit;
 		}
-		return;
+		return null;
 	}
 
 	if ( ! is_object( $wp_filesystem ) ) {

src/wp-admin/includes/theme.php

@@ -40,7 +40,7 @@ function delete_theme( $stylesheet, $redirect = '' ) {
 			require_once ABSPATH . 'wp-admin/admin-footer.php';
 			exit;
 		}
-		return;
+		return null;
 	}
 
 	if ( ! WP_Filesystem( $credentials ) ) {
@@ -55,7 +55,7 @@ function delete_theme( $stylesheet, $redirect = '' ) {
 			require_once ABSPATH . 'wp-admin/admin-footer.php';
 			exit;
 		}
-		return;
+		return null;
 	}
 
 	if ( ! is_object( $wp_filesystem ) ) {

src/wp-includes/category.php

@@ -144,7 +144,7 @@ function get_category_by_path( $category_path, $full_match = true, $output = OBJ
 	);
 
 	if ( empty( $categories ) ) {
-		return;
+		return null;
 	}
 
 	foreach ( $categories as $category ) {