Merge branch '4.1' into 4.2

* 4.1:
  the string "0" is a valid service identifier
  remove unreachable code
  updated MimeType extensions

Author: fabpot

Loader/XmlFileLoader.php

@@ -497,7 +497,7 @@ private function getArgumentsAsPhp(\DOMElement $node, $name, $file, $lowercase =
 
             switch ($arg->getAttribute('type')) {
                 case 'service':
-                    if (!$arg->getAttribute('id')) {
+                    if ('' === $arg->getAttribute('id')) {
                         throw new InvalidArgumentException(sprintf('Tag "<%s>" with type="service" has no or empty "id" attribute in "%s".', $name, $file));
                     }
 
@@ -561,7 +561,7 @@ private function getArgumentsAsPhp(\DOMElement $node, $name, $file, $lowercase =
      * @param \DOMNode $node
      * @param mixed    $name
      *
-     * @return array
+     * @return \DOMElement[]
      */
     private function getChildren(\DOMNode $node, $name)
     {

Tests/Fixtures/xml/services6.xml

@@ -61,5 +61,9 @@
     </service>
     <service id="alias_for_foo" alias="foo" />
     <service id="another_alias_for_foo" alias="foo" public="false" />
+    <service id="0" class="FooClass" />
+    <service id="1" class="FooClass">
+      <argument type="service" id="0" />
+    </service>
   </services>
 </container>