Not all fields of errors are present
In xproto, all errors have bad_value, minor_opcode and major_opcode fields:
https://gitlab.freedesktop.org/xorg/proto/xcbproto/-/blob/7d58eed95f796fc764741d7549ee2214bbbcc64c/src/xproto.xml#L1109-1114
However, some extensions do not, e.g.: https://gitlab.freedesktop.org/xorg/proto/xcbproto/-/blob/7d58eed95f796fc764741d7549ee2214bbbcc64c/src/randr.xml#L44-47
I just followed the code in the X11 server and it seems like all errors always have these fields. Thus, the XML should be fixed accordingly. This is the relevant function that always adds these fields: https://gitlab.freedesktop.org/xorg/xserver/-/blob/d6558477d7a264c2132bc977b51d80fc0277d1e0/dix/dispatch.c#L3740-3753
(This was originally found in https://github.com/psychon/x11rb/issues/503)