[storage] improvement: use null coalescing operator

Author: connorhu

lib/storage/sfCacheSessionStorage.class.php

@@ -176,13 +176,7 @@ public function write($key, $data)
      */
     public function read($key)
     {
-        $retval = null;
-
-        if (isset($this->data[$key])) {
-            $retval = &$this->data[$key];
-        }
-
-        return $retval;
+        return $this->data[$key] ?? null;
     }
 
     /**

lib/storage/sfSessionStorage.class.php

@@ -105,13 +105,7 @@ public function initialize($options = null)
      */
     public function read($key)
     {
-        $retval = null;
-
-        if (isset($_SESSION[$key])) {
-            $retval = $_SESSION[$key];
-        }
-
-        return $retval;
+        return $_SESSION[$key] ?? null;
     }
 
     /**

lib/storage/sfSessionTestStorage.class.php

@@ -74,13 +74,7 @@ public function getSessionId()
      */
     public function read($key)
     {
-        $retval = null;
-
-        if (isset($this->sessionData[$key])) {
-            $retval = $this->sessionData[$key];
-        }
-
-        return $retval;
+        return $this->sessionData[$key] ?? null;
     }
 
     /**