Merge branch '5.2' into 5.x

* 5.2:
  [Notifier] Rework/streamline bridges (5.1)
  [Mailer] [Amazon] Ensure "ext-simplexml" is loaded if SesApiTransport is used
  Stop using deprecated trait
  [PhpUnitBridge] Lint files with PHP 5.5

Author: derrabus

ClassExistsMock.php

@@ -30,17 +30,23 @@ public static function withMockedClasses(array $classes)
 
     public static function class_exists($name, $autoload = true)
     {
-        return (bool) (self::$classes[ltrim($name, '\\')] ?? \class_exists($name, $autoload));
+        $name = ltrim($name, '\\');
+
+        return isset(self::$classes[$name]) ? (bool) self::$classes[$name] : \class_exists($name, $autoload);
     }
 
     public static function interface_exists($name, $autoload = true)
     {
-        return (bool) (self::$classes[ltrim($name, '\\')] ?? \interface_exists($name, $autoload));
+        $name = ltrim($name, '\\');
+
+        return isset(self::$classes[$name]) ? (bool) self::$classes[$name] : \interface_exists($name, $autoload);
     }
 
     public static function trait_exists($name, $autoload = true)
     {
-        return (bool) (self::$classes[ltrim($name, '\\')] ?? \trait_exists($name, $autoload));
+        $name = ltrim($name, '\\');
+
+        return isset(self::$classes[$name]) ? (bool) self::$classes[$name] : \trait_exists($name, $autoload);
     }
 
     public static function register($class)