Thread.start() suddenly doesn't accept NULL (either as default or specified) userdata variable?

[sszigeti]

Godot version

3.4.beta3

System information

Windows 10

Issue description

I'm using Thread.start() to load static data for my game, like so:

var _thread = Thread.new()

func start_loading():
    _thread.start(self, "_load_my_data")

func _load_my_data(_unused_but_mandatory_thread_arg):
    # here I'm loading my data
    pass

This was working perfectly at least since 3.2, including 3.3.stable, however with 3.4.beta3 I get this error:

E 0:00:00.724   _start_func: Could not call function '_load_my_data' to start thread -8534501772636260605: Too Few Arguments.
  <C++ Error>   Method failed.
  <C++ Source>  core/bind/core_bind.cpp:2673 @ _start_func()

If I modify my code by specifying the 3rd argument for the Thread.start, the error doesn't show and my code completes as expected:

    _thread.start(self, "_load_my_data", 1)

Passing null (instead of 1) also invokes the error, so I'm guessing Thread.start's userdata argument no longer has a default null value, and/or no longer accepts a null value.

Steps to reproduce

Try to start a thread by only passing the first 2 mandatory arguments to Thread.start(). You'll find that now you also must pass a non-null 3rd argument.

Minimal reproduction project

Thread_start_3rd_arg_bug_demo.zip

[akien-mga]

Just tested with #51574, this was fixed in #51385 (will be in 3.4 beta 4).

[RandomShaper]

This should hav been fixed by #51093 + #51385 + their cherry-picks to 3.x. I don't know which of them made to the beta. Furthermore, I'm failing to find the cherry-pick of the latter in the 3.x branch.

[akien-mga]

Furthermore, I'm failing to find the cherry-pick of the latter in the 3.x branch.

Yeah it was still queued in my local branch, now it's in #51574.

[RandomShaper]

Oh, we did concurrent posting. 😀

Aside, I forgot that the cherry-pick mechanics are to create a batch of them. That explains why I couldn't find it.