[Bridge][Twig] DebugCommand - fix escaping and filter

Author: SpacePossum

Tester/CommandTester.php

@@ -87,6 +87,10 @@ public function execute(array $input, array $options = [])
      */
     public function getDisplay($normalize = false)
     {
+        if (null === $this->output) {
+            throw new \RuntimeException('Output not initialized, did you execute the command before requesting the display?');
+        }
+
         rewind($this->output->getStream());
 
         $display = stream_get_contents($this->output->getStream());