Update Transformers to comply with MastoAPI

app/Transformer/ActivityPub/StatusTransformer.php

@@ -11,7 +11,7 @@ class StatusTransformer extends Fractal\TransformerAbstract
 {
     public function transform(Status $status)
     {
-        $content = $status->caption ? nl2br(Autolink::create()->autolink($status->caption)) : null;
+        $content = $status->caption ? nl2br(Autolink::create()->autolink($status->caption)) : "";
 
         return [
             '@context' => [

app/Transformer/ActivityPub/Verb/CreateNote.php

@@ -52,7 +52,7 @@ class CreateNote extends Fractal\TransformerAbstract
         $emojis = CustomEmoji::scan($status->caption, true) ?? [];
         $emoji = array_merge($emojis, $mentions);
         $tags = array_merge($emoji, $hashtags);
-        $content = $status->caption ? nl2br(Autolink::create()->autolink($status->caption)) : null;
+        $content = $status->caption ? nl2br(Autolink::create()->autolink($status->caption)) : "";
 
         return [
             '@context' => [

app/Transformer/ActivityPub/Verb/Note.php

@@ -53,7 +53,7 @@ class Note extends Fractal\TransformerAbstract
         $emojis = CustomEmoji::scan($status->caption, true) ?? [];
         $emoji = array_merge($emojis, $mentions);
         $tags = array_merge($emoji, $hashtags);
-        $content = $status->caption ? nl2br(Autolink::create()->autolink($status->caption)) : null;
+        $content = $status->caption ? nl2br(Autolink::create()->autolink($status->caption)) : "";
 
         return [
             '@context' => [

app/Transformer/ActivityPub/Verb/UpdateNote.php

@@ -53,7 +53,7 @@ class UpdateNote extends Fractal\TransformerAbstract
         $emoji = array_merge($emojis, $mentions);
         $tags = array_merge($emoji, $hashtags);
 
-        $content = $status->caption ? nl2br(Autolink::create()->autolink($status->caption)) : null;
+        $content = $status->caption ? nl2br(Autolink::create()->autolink($status->caption)) : "";
         $latestEdit = $status->edits()->latest()->first();
 
         return [

app/Transformer/Api/Mastodon/v1/StatusTransformer.php

@@ -13,7 +13,7 @@ class StatusTransformer extends Fractal\TransformerAbstract
 {
     public function transform(Status $status)
     {
-        $content = $status->caption ? nl2br(Autolink::create()->autolink($status->caption)) : null;
+        $content = $status->caption ? nl2br(Autolink::create()->autolink($status->caption)) : "";
 
         return [
             'id' => (string) $status->id,

app/Transformer/Api/StatusTransformer.php

@@ -25,7 +25,7 @@ class StatusTransformer extends Fractal\TransformerAbstract
         $pid = request()->user()->profile_id;
         $taggedPeople = MediaTagService::get($status->id);
         $poll = $status->type === 'poll' ? PollService::get($status->id, $pid) : null;
-        $content = $status->caption ? nl2br(Autolink::create()->autolink($status->caption)) : null;
+        $content = $status->caption ? nl2br(Autolink::create()->autolink($status->caption)) : "";
 
         return [
             '_v' => 1,