Godot: Configuration warning text not showing on editor.

[luizcarlos1405]

Godot version:
3.1 beta 6

OS/device including version:
Linux Ubuntu 18.04

Issue description:
As title:

Steps to reproduce:

extends Node

func _get_configuration_warning() -> String:
    return "Cool warning."

Minimal reproduction project:
warning bug.zip

[luizcarlos1405]

The line 2661 returns Null here, couldn't figure out why.

https://github.com/godotengine/godot/blob/9d78274e068d4928044220c4d5c1a7baed423670/scene/main/node.cpp#L2658-L2664

[akien-mga]

You need to make this a tool script for it to run in the editor.

But there's an inconsistency nevertheless, as it does show a configuration warning with Null when it's not a tool script. It should either not show a configuration warning at all, or show the correct one.