### Godot version

v4.1.rc2.official [46424488e]

### System information

Godot v4.1.rc2 - Windows 10.0.22621 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3060 (NVIDIA; 31.0.15.3623) - AMD Ryzen 7 5700G with Radeon Graphics (16 Threads)

### Issue description

When setting the AnimationTree to active, Godot crashes.

### Steps to reproduce

https://github.com/godotengine/godot/assets/46705245/dbe5eb81-1357-43e8-ac80-a4eb97eea9fc

### Minimal reproduction project

[Crash.zip](https://github.com/godotengine/godot/files/11945826/Crash.zip)

ERR_FAIL_COND_V_MSG(group_start_transition.is_null(), Ref<AnimationNodeStateMachineTransition>(), "Group start transition is null.");
	return group_start_transition;
}
Ref<AnimationNodeStateMachineTransition> AnimationNodeStateMachinePlayback::_get_group_end_transition() const {
	ERR_FAIL_COND_V_MSG(group_end_transition.is_null(), Ref<AnimationNodeStateMachineTransition>(), "Group end transition is null.");
	return group_end_transition;
}
void AnimationNodeStateMachinePlayback::_bind_methods() {
	ClassDB::bind_method(D_METHOD("travel", "to_node", "reset_on_teleport"), &AnimationNodeStateMachinePlayback::travel, DEFVAL(true));
	ClassDB::bind_method(D_METHOD("start", "node", "reset"), &AnimationNodeStateMachinePlayback::start, DEFVAL(true));
	ClassDB::bind_method(D_METHOD("next"), &AnimationNodeStateMachinePlayback::next);
	ClassDB::bind_method(D_METHOD("stop"), &AnimationNodeStateMachinePlayback::stop);
	ClassDB::bind_method(D_METHOD("is_playing"), &AnimationNodeStateMachinePlayback::is_playing);
	ClassDB::bind_method(D_METHOD("get_current_node"), &AnimationNodeStateMachinePlayback::get_current_node);
	ClassDB::bind_method(D_METHOD("get_current_play_position"), &AnimationNodeStateMachinePlayback::get_current_play_pos);
	ClassDB::bind_method(D_METHOD("get_current_length"), &AnimationNodeStateMachinePlayback::get_current_length);
	ClassDB::bind_method(D_METHOD("get_fading_from_node"), &AnimationNodeStateMachinePlayback::get_fading_from_node);
	ClassDB::bind_method(D_METHOD("get_travel_path"), &AnimationNodeStateMachinePlayback::_get_travel_path);
}
AnimationNodeStateMachinePlayback::AnimationNodeStateMachinePlayback() {