Issue 11846: Fix client behaviour when following hash tags

src/Content/Text/BBCode.php

@@ -1975,6 +1975,9 @@ class BBCode
 					$text = preg_replace("/([@!])\[url\=(.*?)\](.*?)\[\/url\]/ism",
 						'<bdi>$1<a href="$2" class="userinfo mention" title="$3">$3</a></bdi>',
 						$text);
+					$text = preg_replace("/([#])\[url\=(.*?)\](.*?)\[\/url\]/ism",
+						'<a class="mention hashtag status-link" href="$2" rel="tag">$1<span>$3</span></a>',
+						$text);
 				} else {
 					$text = preg_replace("/([#@!])\[url\=(.*?)\](.*?)\[\/url\]/ism", '$1$3', $text);
 				}

src/Object/Api/Mastodon/Status.php

@@ -109,7 +109,7 @@ class Status extends BaseDataTransferObject
 		}
 
 		$this->sensitive    = $sensitive;
-		$this->spoiler_text = $item['title'] ?: $item['content-warning'];
+		$this->spoiler_text = ($item['title'] ?: $item['content-warning']) ?: '';
 
 		$visibility = ['public', 'private', 'unlisted'];
 		$this->visibility = $visibility[$item['private']];