Fix PossiblyNullPropertyAssignmentValue issues

Author: morozov

lib/Doctrine/DBAL/Schema/TableDiff.php

@@ -10,7 +10,7 @@
 class TableDiff
 {
     /** @var string */
-    public $name = null;
+    public $name;
 
     /** @var string|false */
     public $newName = false;