[libxml++] question about Document::set_entity_declaration()

[Kike Fernandez <sisfetek si ehu es>]

Hello,

Is there a way to create an entity declaration of this type with
Document::set_entity_declaration() function?

<!ENTITY TDoc01 SYSTEM "proba.xml" NDATA CorpusId>

set_entity_declaration() takes five arguments, one of which is the
publicId. In libxml I can pass a NULL pointer as publicId so the library
creates correctly the entity but in libxml++ I cannot pass a NULL
pointer (I get "Exception caught: attempt to create string with null
pointer") and passing an empty string always creates something like 

<!ENTITY TDoc01 PUBLIC "" "proba.xml" NDATA CorpusId> 

Am I doing something wrong or is this a bug? 

Thank you.

-- 
Kike Fernandez <sisfetek si ehu es>
IXA Taldea