Merge pull request #8505 from creative-commoners/pulls/4.3/defensive-extensions

FIX getExtensionInstance can return null, add a case to handle that

src/Core/Extensible.php

@@ -135,6 +135,10 @@ trait Extensible
                 $this->addCallbackMethod($method, function ($inst, $args) use ($method, $extensionClass) {
                     /** @var Extensible $inst */
                     $extension = $inst->getExtensionInstance($extensionClass);
+                    if (!$extension) {
+                        return null;
+                    }
+
                     try {
                         $extension->setOwner($inst);
                         return call_user_func_array([$extension, $method], $args);

src/Dev/State/ExtensionTestState.php

@@ -85,5 +85,6 @@ class ExtensionTestState implements TestState
 
     public function tearDownOnce($class)
     {
+        DataObject::flush_extra_methods_cache();
     }
 }