Add the @return types

src/Sse.php

@@ -309,7 +309,7 @@ class Sse
   /** Initialize the backend for one specific file.
     * @param string $event The event to start
     * @param string $filePath The file path where the event data are stored
-    * @return false if the file doesn't exists
+    * @return boolean false if the file doesn't exists
     */
   private function backendInitEvent ($event, $filePath)
   // {{{