Exmpp question

While migrating an existing module from 2.x to 3.x, I am getting the following error:

** Reason for termination =
** {function_clause,
[{exmpp_xml,xmlnsattributes_to_xmlattributes2,
[{xmlattr,undefined,<<"var">>,<<"device">>},
[{'http://etherx.jabber.org/streams',"stream"},
{'jabber:server:dialback',"db"}],
[]]},
{exmpp_xml,unresolve_xmlel_nss,3},
{exmpp_xml,node_to_iolist2,4},
{exmpp_xml,element_to_iolist,5},
{exmpp_xml,node_to_iolist2,4},
{exmpp_xml,element_to_iolist,5},
{exmpp_xml,node_to_iolist2,4},
{ejabberd_c2s,send_element,2}]}

Looks like using exmpp_xml:attribute(Name, Value) creates #xmlattr with ns = undefined. Should that not get stripped out by the underlying library or is the expectation that every attribute and element needs to provide the NS?