Merge branch '3.0'

* 3.0:
  The exception should be thrown if an object doesn't implement Traversable AND doesn't implement Countable, not when it doesn't implement Traversable but DOES implement Countable
  [Form] fix violation mapper tests
  [HttpKernel] Prevent a fatal error when DebugHandlersListener is used with a kernel with no terminateWithException() method
  don't rely on deprecated YAML parser feature

Author: fabpot

Question/Question.php

@@ -143,7 +143,7 @@ public function setAutocompleterValues($values)
         }
 
         if (null !== $values && !is_array($values)) {
-            if (!$values instanceof \Traversable || $values instanceof \Countable) {
+            if (!$values instanceof \Traversable || !$values instanceof \Countable) {
                 throw new InvalidArgumentException('Autocompleter values can be either an array, `null` or an object implementing both `Countable` and `Traversable` interfaces.');
             }
         }