hide domelight alpha channel(Solaris)

[saca]

hi,
in solaris with Arnold,
domelight fills  alpha channel full.
HDRI use or no use, it's no relation, always fill alpha.

i heard, Mantra has the option hide light-geo.

if you know please tell me,in solaris,  how to hide domelight in aplha channel?
if can do it , show rgb the environment color, only off alpha for tranparecy area.

thanks
 

[saca]

avoiding this ploblem with below technique.
adding Huge Dome(or Sphere) for Matting.(hope infinit geometry...)
And RenderGeoSettings(Arnold/visibility) is CamerarayVis=On, Matte=On, others Off.
no shader.

domelight HDRI Alpha has bugs?

please tell me any if you know.

thanks