Godot headless prints several "ERROR: VisualServer attempted to free a NULL RID."

[Kazuo256]

Godot version

v3.6.beta2 [68c507f]

System information

Manjaro XFCE and Ubuntu Focal (docker)

Issue description

When running the Linux x64 headless build, Godot prints this error message several times when closing:

ERROR: VisualServer attempted to free a NULL RID.
   at: free (servers/visual/visual_server_raster.cpp:69)

It does not crash (non-zero exit), though.

Steps to reproduce

Download Godot 3.6 beta 2's Linux x64 headless build and run the script below with:

godot -s example.gd

Also seems to happen in 3.6 beta 3. Did not test in beta 1, but was not happening as far as 3.5.1.

Minimal reproduction project

extends SceneTree

func _init():
	quit()

[lawnjelly]

This likely happened before exactly the same, but the output of an error message was added in #55764, #64234 .

This may not be an error, some of these were probably benign, but @TokisanGames was keen to add error messages.
Will need debugging to find out whether this is a genuine error or a false flag.

See particularly my comment here:
#55764 (comment)

About dummy servers creating NULL RIDs by design.
(I remain sceptical of the benefit BTW, I personally probably wouldn't create error messages for NULL RIDs, because you end up having to add extra code to prevent calling the free function, and I'm not convinced it helps pinpoint bugs. Malloc for example doesn't error on passing NULL. 4.x also does not generate an error message when passed NULL RID.)