Fix XML unserializer

The subNodes array was not initialized, so for empty nodes it would just
be null. Due to the addition of attributes for nodes those have to be
initialized too.

lib/PHPParser/Unserializer/XML.php

@@ -47,7 +47,10 @@ class PHPParser_Unserializer_XML implements PHPParser_Unserializer
 
         // create the node without calling it's constructor
         $node = unserialize(
-            sprintf('O:%d:"%s":0:{}', strlen($className), $className)
+            sprintf(
+                "O:%d:\"%s\":2:{s:11:\"\0*\0subNodes\";a:0:{}s:13:\"\0*\0attributes\";a:0:{}}",
+                strlen($className), $className
+            )
         );
 
         $line = $this->reader->getAttribute('line');

test/PHPParser/Tests/Unserializer/XMLTest.php

@@ -21,6 +21,21 @@ XML;
         );
     }
 
+    public function testEmptyNode() {
+        $xml = <<<XML
+<?xml version="1.0" encoding="UTF-8"?>
+<AST xmlns:node="http://nikic.github.com/PHPParser/XML/node" xmlns:subNode="http://nikic.github.com/PHPParser/XML/subNode" xmlns:scalar="http://nikic.github.com/PHPParser/XML/scalar">
+ <node:Scalar_ClassConst />
+</AST>
+XML;
+
+        $unserializer  = new PHPParser_Unserializer_XML;
+        $this->assertEquals(
+            new PHPParser_Node_Scalar_ClassConst,
+            $unserializer->unserialize($xml)
+        );
+    }
+
     public function testScalars() {
         $xml = <<<XML
 <?xml version="1.0" encoding="UTF-8"?>