Minor, refer to Method.UNKNOWN rather than
org.apache.xml.serializer.Method.UNKNOWN.

That class and this one are in the same package, so it isn't needed.
diff --git a/src/org/apache/xml/serializer/OutputPropertiesFactory.java b/src/org/apache/xml/serializer/OutputPropertiesFactory.java
index 500b8dd..89b5ad4 100644
--- a/src/org/apache/xml/serializer/OutputPropertiesFactory.java
+++ b/src/org/apache/xml/serializer/OutputPropertiesFactory.java
@@ -298,7 +298,7 @@
 
                 defaultProperties = m_text_properties;
             }
-            else if (method.equals(org.apache.xml.serializer.Method.UNKNOWN))
+            else if (method.equals(Method.UNKNOWN))
             {
                 if (null == m_unknown_properties) // double check
                 {