### 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)

return advance_condition;
}
StringName AnimationNodeStateMachineTransition::get_advance_condition_name() const {
	return advance_condition_name;
}
void AnimationNodeStateMachineTransition::set_advance_expression(const String &p_expression) {
	advance_expression = p_expression;
	String advance_expression_stripped = advance_expression.strip_edges();
	if (advance_expression_stripped == String()) {
		expression.unref();
		return;
	}
	if (expression.is_null()) {
		expression.instantiate();
	}
	expression->parse(advance_expression_stripped);
}
String AnimationNodeStateMachineTransition::get_advance_expression() const {
	return advance_expression;
}
void AnimationNodeStateMachineTransition::set_xfade_time(float p_xfade) {