xpath with an namespace:attribute not working in XPathEntityProcessor

I would like to use attributes originaly with namespaces. E.g. i have two main tags:

<dc:contributor xml:lang="cz">John Doe</dc:contributor>
<dc:contributor lang="en">Mark Tester</dc:contributor>

Field definition, where I remove namespaces, is
<field column="attr_myTest" xpath="/metadata/contributor/@lang"/>

The result of the extraction is (extracted only one attribute):
"attr_myTest": ["en"]
but the expected result should be extracted all two attributes:
"attr_myTest": ["cz", "en"]

I would like to ask you to implement a patch to be able to use attributes with namespaces in original XML. For tag names removing namespaces works fine. Thanks a lot!