Fixed some phpstan errors

src/Group/ConnectionGroup.php

@@ -46,11 +46,19 @@ class ConnectionGroup implements EventEmitterInterface, IteratorAggregate, Count
         return count($this->connections);
     }
 
+    /** 
+     * 
+     * @return \Traversable<int,WebSocketInterface> 
+     */
     public function getIterator(): Traversable
     {
         return new ArrayIterator($this->connections);
     }
 
+    /**
+     * 
+     * @return WebSocketInterface[]
+     */
     public function getAll(): array
     {
         return $this->connections;
@@ -70,6 +78,10 @@ class ConnectionGroup implements EventEmitterInterface, IteratorAggregate, Count
         }
     }
 
+    /**
+     * 
+     * @return void
+     */
     public function closeAll(string $reason, int $code=1001)
     {
         foreach ($this->connections as $connection) {

src/WebSocketMiddleware.php

@@ -64,7 +64,8 @@ class WebSocketMiddleware implements EventEmitterInterface
             $this->emit(self::EVENT_CONNECTION, [ $websocket ]);
         //});
 
-        // TODO would it be possible or rather useful for the 'connection' event to set additional response headers to be sent here?
+        // TODO would it be possible for the 'connection' event to set additional response headers to be sent here?
+        // For example, to send back Sec-WebSocket-Protocol header.
         return new Response(
             Response::STATUS_SWITCHING_PROTOCOLS,
             array(

src/WebSocketProtocol.php

@@ -111,7 +111,7 @@ class WebSocketProtocol
      *   payload (string) - the payload
      * 
      * @param string $frame The frame data to decode
-     * @return array The decoded frame
+     * @return array<string,mixed> The decoded frame
      */
     public function decode(string $frame): array
     {