Merge branch '4.3' into 4.4

* 4.3:
  cs fix
  Fix inconsistent return points.
  [Config] Add handling for ignored keys in ArrayNode::mergeValues.
  Fix inconsistent return points.
  [Security/Core] UserInterface::getPassword() can return null
  [Router] Fix TraceableUrlMatcher behaviour with trailing slash
  Revert "bug #33092 [DependencyInjection] Improve an exception message (fabpot)"

Author: nicolas-grekas

Constraints/AbstractComparisonValidator.php

@@ -117,5 +117,6 @@ abstract protected function compareValues($value1, $value2);
      */
     protected function getErrorCode()
     {
+        return null;
     }
 }

Tests/Constraints/AbstractComparisonValidatorTestCase.php

@@ -266,5 +266,6 @@ abstract protected function createConstraint(array $options = null);
      */
     protected function getErrorCode()
     {
+        return null;
     }
 }