Correct PHPDoc type for float ttl

It can be null as the Lock instance accepts it.

Author: soullivaneuh

src/Symfony/Component/Lock/Factory.php

@@ -36,9 +36,9 @@ public function __construct(StoreInterface $store)
     /**
      * Creates a lock for the given resource.
      *
-     * @param string $resource    The resource to lock
-     * @param float  $ttl         Maximum expected lock duration in seconds
-     * @param bool   $autoRelease Whether to automatically release the lock or not when the lock instance is destroyed
+     * @param string     $resource    The resource to lock
+     * @param float|null $ttl         Maximum expected lock duration in seconds
+     * @param bool       $autoRelease Whether to automatically release the lock or not when the lock instance is destroyed
      *
      * @return Lock
      */