Issue #3274273: Fix deprecation errors on PHP 8.1

package_manager/src/EventSubscriber/ExcludedPathsSubscriber.php

@@ -114,7 +114,7 @@ class ExcludedPathsSubscriber implements EventSubscriberInterface {
 
     foreach ($paths as $path) {
       // Make absolute paths relative to the project root.
-      $path = str_replace($project_root, NULL, $path);
+      $path = str_replace($project_root, '', $path);
       $path = ltrim($path, '/');
       $event->excludePath($path);
     }

package_manager/src/PathLocator.php

@@ -60,7 +60,7 @@ class PathLocator {
    *   project root and Drupal root are the same.
    */
   public function getWebRoot(): string {
-    $web_root = str_replace($this->getProjectRoot(), NULL, $this->appRoot);
+    $web_root = str_replace($this->getProjectRoot(), '', $this->appRoot);
     return trim($web_root, DIRECTORY_SEPARATOR);
   }
 

tests/src/Build/CoreUpdateTest.php

@@ -170,7 +170,7 @@ class CoreUpdateTest extends UpdateTestBase {
     $workspace_dir = $this->getWorkspaceDirectory();
 
     // Loop through core's metapackages and plugins, and alter them as needed.
-    $packages = str_replace("$workspace_dir/", NULL, $this->getCorePackages());
+    $packages = str_replace("$workspace_dir/", '', $this->getCorePackages());
     foreach ($packages as $path) {
       // Assign the new upstream version.
       $this->runComposer("composer config version $version", $path);