[Vala] Problem with create vapi file

["d3ny ..." <d3ny 90 gmail com>]

Hello everyone!

I try to create vapi files for libgrss, because I would like to use
this library in my apps.
libgrss is a GObject library intended to be used to manage syndication
feeds in convenient way (from reference manual).
But I get receive error in vapigen. I describe all what I did.

Firstly, my Vala version:
$ valac --version
Vala 0.10.4

I generate the gi file with vala-gen-introspect:
$ vala-gen-introspect libgrss-0 vapi
Unknown symbol: GObject
Unknown symbol: GObject
Unknown symbol: GObject
Unknown symbol: GObject
Unknown symbol: GObject
Unknown symbol: GObject
Unknown symbol: GObject
Unknown symbol: GObject

'libgrss-0' is the file in my pkgconfig folder and 'vapi' is the
folder, where I have 'namespace & files' file.
-libgrss-0.files:
/usr/include/libgrss/
/usr/lib/libgrss-1.0.so
-libgrss-0.namespace:
GRss

Then I try to generate vapi file:
$ vapigen --pkg=libxml-2.0 --pkg=libsoup-2.4 --pkg=gobject-2.0
--library libgrss vapi/libgrss-0.gi
error: The type name `xmlDocPtr' could not be found
Generation failed: 1 error(s), 0 warning(s)

I dont know why I get this error, because I add package libxml-2.0.
Could samone help me with this problem?

Thanks in advance, Daniel K.