Fix Json renderer with empty changes

Signed-off-by: Jack Cherng <jfcherng@gmail.com>

Author: jfcherng

src/Renderer/Html/Json.php

@@ -30,6 +30,10 @@ public function render(): string
     {
         $changes = $this->getChanges();
 
+        if (empty($changes)) {
+            return self::getIdenticalResult();
+        }
+
         if ($this->options['outputTagAsString']) {
             $this->convertTagToString($changes);
         }
@@ -40,6 +44,14 @@ public function render(): string
         );
     }
 
+    /**
+     * {@inheritdoc}
+     */
+    public static function getIdenticalResult(): string
+    {
+        return '[]';
+    }
+
     /**
      * Convert tags of changes to their string form for better readability.
      *