GUPnPDIDLLiteObject has getters for the XML namespaces:

gupnp_didl_lite_object_get_upnp_namespace()
gupnp_didl_lite_object_get_dc_namespace()
gupnp_didl_lite_object_get_dlna_namespace()
gupnp_didl_lite_object_get_pv_namespace()

These are intented for third-party code that needs access to these namespaces in order to enrich the DIDL-Lite XML fragment.

With the changes that went into 0.12.6 the namespace handling was changed considerably so that namespaces are now created lazily. This creates two problems:

(1) The namespace getters will return NULL if they are used before another
    internal function has created the namespace.
(2) The optimization that namespaces are not created for each object but
    shared across all objects created by the same GUPnPDIDLLiteWriter is gone.

I am attaching two patches. One adds a unit test for the namespace getters. The second patch fixes problem (1). Problem (2) remains open for now, but it's just a missing optimization and does not really count as a bug. So it has lower priority and can be addressed later.