Merge branch '5.4' into 6.4

* 5.4:
  do not mix named and positional arguments in data provider definitions
  session names must not be empty
  fix Contracts directory name in PHPUnit configuration
  Passing null to parameter #2 ($subject) of type string is deprecated

Author: xabbuh

Tests/Session/Storage/Handler/AbstractRedisSessionHandlerTestCase.php

@@ -89,7 +89,7 @@ public function testUseSessionGcMaxLifetimeAsTimeToLive()
 
     public function testDestroySession()
     {
-        $this->storage->open('', '');
+        $this->storage->open('', 'test');
         $this->redisClient->set(self::PREFIX.'id', 'foo');
 
         $this->assertTrue((bool) $this->redisClient->exists(self::PREFIX.'id'));

Tests/Session/Storage/Handler/MemcachedSessionHandlerTest.php

@@ -109,7 +109,7 @@ public function testWriteSessionWithLargeTTL()
 
     public function testDestroySession()
     {
-        $this->storage->open('', '');
+        $this->storage->open('', 'sid');
         $this->memcached
             ->expects($this->once())
             ->method('delete')