[Axis2][Axiom] Correct behavior for the getNamespace method

Hi all,
I've found that the cause of numerous bug reports concerning the
deserililzation of XMLBeans is actually an issue with the
getNamespaceURI(int index) method of the pullparser where it returns
null for the empty namespace URI. XMLBeans assumes the uri is never
null but the reader implementations (including the wstx implementation
that we use inside Axis2) return null for the empty namespace URI. I
can work around the bug but this is one fine point that should get
very clear about :)

The Javadoc for XMLStreamReader is silent on this
(https://stax-utils.dev.java.net/nonav/javadoc/api/javax/xml/stream/XMLStreamReader.html#getNamespaceURI(int))
but since the empty namespace is decalred with an empty string, I
would say it should return an empty string rather than a null!

Thoughts ?

-- 
Ajith Ranabahu

PS - From a very quick test I've found out that the change occurred in
the transition of wstx version 2.8 to 2.9  - wstx 2.8.* returns "" but
2.9.* returns null!.