XMLBEANS-506: use thread context classloader if loader is null

git-svn-id: https://svn.apache.org/repos/asf/xmlbeans/trunk@1844289 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/src/xmlpublic/org/apache/xmlbeans/XmlBeans.java b/src/xmlpublic/org/apache/xmlbeans/XmlBeans.java
index 14bbe64..f44b623 100644
--- a/src/xmlpublic/org/apache/xmlbeans/XmlBeans.java
+++ b/src/xmlpublic/org/apache/xmlbeans/XmlBeans.java
@@ -766,7 +766,8 @@
     {
         try
         {
-            Class clazz = loader.loadClass(stsName + "." + HOLDER_CLASS_NAME);
+            ClassLoader cl = loader == null ? Thread.currentThread().getContextClassLoader() : loader;
+            Class clazz = cl.loadClass(stsName + "." + HOLDER_CLASS_NAME);
             SchemaTypeSystem sts = (SchemaTypeSystem)
                 (clazz.getDeclaredField(TYPE_SYSTEM_FIELD).get(null));
             if (sts == null)