[BUGFIX] Trim whitespaces in JSON decode helper (#603)

Classes/ViewHelpers/Format/Json/DecodeViewHelper.php

@@ -33,6 +33,9 @@ public function render()
         $json = $this->arguments['json'];
         if ($json === null) {
             $json = $this->renderChildren();
+            if ($json !== null) {
+                $json = trim($json);
+            }
             if (empty($json)) {
                 return null;
             }

Tests/Unit/ViewHelpers/Format/Json/DecodeViewHelperTest.php

@@ -0,0 +1,28 @@
+<?php
+
+/*
+ * This file is part of the "headless" Extension for TYPO3 CMS.
+ *
+ * For the full copyright and license information, please read the
+ * LICENSE.md file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace FriendsOfTYPO3\Headless\Tests\Unit\ViewHelpers\Format\Json;
+
+use FriendsOfTYPO3\Headless\ViewHelpers\Format\Json\DecodeViewHelper;
+use TYPO3\TestingFramework\Core\Unit\UnitTestCase;
+
+class DecodeViewHelperTest extends UnitTestCase
+{
+    public function testRender(): void
+    {
+        $GLOBALS['TYPO3_CONF_VARS']['FE']['debug'] = true;
+        $decodeViewHelper = new DecodeViewHelper();
+        $decodeViewHelper->setArguments(['json' => null]);
+        $decodeViewHelper->setRenderChildrenClosure(function () { return "\n \n"; });
+        $result = $decodeViewHelper->render();
+        self::assertNull($result);
+    }
+}