Merge branch '2.8' into 3.0

* 2.8:
  [2.7] Fix tests
  pass triggerDeprecationError arg to parent class
  remove default null value for asset version
  remove duplicated value
  [Ldap] Remove unused private property
  Update UPGRADE-3.0 with correct Voter details
  Change few occurences of a public setUp() method to protected
  [DependencyInjection] simplify the BC layer
  Change couple of occurences of a public setUp() method to protected

Author: fabpot

DependencyInjection/Configuration.php

@@ -396,7 +396,6 @@ private function addAssetsSection(ArrayNodeDefinition $rootNode)
                                 ->fixXmlConfig('base_url')
                                 ->children()
                                     ->scalarNode('version')
-                                        ->defaultNull()
                                         ->beforeNormalization()
                                         ->ifTrue(function ($v) { return '' === $v; })
                                         ->then(function ($v) { return; })