doclets/gtkdoclet: FormalParameter: Fix null ptr warning triggered by generic types
doclets/gtkdoclet: FormalParameter: Fix null ptr warning triggered by generic types

GNOME/vala,frida/vala,frida/vala,frida/vala,GNOME/vala,frida/vala,frida/vala,GNOME/vala,GNOME/vala