Starting a thread from GDScript always require non-null data to be passed

[m4nu3lf]

Godot version

3.x build 51f8247

System information

OS: Arch Linux, CPU: Ryzen 5, GUP: RX 480

Issue description

When calling Thread.start() with null data the thread doesn't start and this error is reported:

ERROR: Could not call function 'thread_run' to start thread 5559469359093562243: Too Few Arguments.
   at: _start_func (core/bind/core_bind.cpp:2604)

It used to be possible to not specify the user data parameter and have that default to null.
Forcing the user to pass in some non-null data seems unnecessary.

Steps to reproduce

• Create a scene with a single node and a script for the node.
• Create a thread in the "_ready" method and start it by calling a function on the same script and specifying no data:

var my_thread: Thread = Thread.new()

func thread_run(_data) -> void:
  pass
  
func _ready():
  my_thread.start(self, "thread_run")

Minimal reproduction project

No response

[akien-mga]

Likely a regression from #38078, CC @Faymoon @RandomShaper.

[akien-mga]

I'm not sure that's a bug though, this might just be the consequence of the bugfix.

If there's a parameter without a default value, it must be passed.

Confirmed that it works fine when specifying a fallback value:

var my_thread: Thread = Thread.new()

func thread_run(_data = null) -> void:
  pass
  
func _ready():
  my_thread.start(self, "thread_run")

What would you expect _data to be initialized to if it's not assigned a default value and not passed in the start() call?

[m4nu3lf]

There is null default value defined in the start method as userdata, I would expect that to be used if no data is specified.

start(instance: Object, method: String, userdata: Variant = null, priority: Priority = 1)

I understand it can work that way too, but it is a bit surprising to me.

Also no nulls are allowed unless the target function specifies a default null value too.