Update AccountTransformer

app/Transformer/Api/AccountTransformer.php

@@ -23,8 +23,8 @@ class AccountTransformer extends Fractal\TransformerAbstract
           'url'             => $profile->url(),
           'avatar'          => $profile->avatarUrl(),
           'avatar_static'   => $profile->avatarUrl(),
-          'header'          => '',
-          'header_static'   => '',
+          'header'          => null,
+          'header_static'   => null,
           'moved'           => null,
           'fields'          => null,
           'bot'             => null,