Add braces to name call

src/View/HelperRegistry.php

@@ -91,7 +91,7 @@ class HelperRegistry extends ObjectRegistry implements EventDispatcherInterface
         if (isset($this->_loaded[$name])) {
             return $this->_loaded[$name];
         }
-        if (isset($this->$name)) {
+        if (isset($this->{$name})) {
             return $this->_loaded[$name];
         }