Maybe fix for:

"Argument 1 passed to Friendica\Model\ItemURI::getIdByURI() must be of the type string, null given, called in Processor.php line 1219"

src/Model/ItemURI.php

@@ -65,6 +65,10 @@ class ItemURI
 	 */
 	public static function getIdByURI(string $uri): int
 	{
+		if (empty($uri)) {
+			return 0;
+		}
+
 		// If the URI gets too long we only take the first parts and hope for best
 		$uri = substr($uri, 0, 255);
 

src/Model/Photo.php

@@ -321,7 +321,7 @@ class Photo
 	 * @param string  $filename  Filename
 	 * @param string  $album     Album name
 	 * @param integer $scale     Scale
-	 * @param integer $type      Photo type
+	 * @param integer $type      Photo type, optional, default: Photo::DEFAULT
 	 * @param string  $allow_cid Permissions, allowed contacts. optional, default = ""
 	 * @param string  $allow_gid Permissions, allowed groups. optional, default = ""
 	 * @param string  $deny_cid  Permissions, denied contacts.optional, default = ""

src/Protocol/ActivityPub/Processor.php

@@ -1216,7 +1216,7 @@ class Processor
 		}
 
 		$replyto = JsonLD::fetchElement($activity['as:object'], 'as:inReplyTo', '@id');
-		$uriid = ItemURI::getIdByURI($replyto);
+		$uriid = ItemURI::getIdByURI($replyto ?? '');
 		if (Post::exists(['uri-id' => $uriid])) {
 			Logger::info('Post is a reply to an existing post - accepted', ['id' => $id, 'uri-id' => $uriid, 'replyto' => $replyto]);
 			return true;