Conditional drawers not considering null as a valid comparison

[Vacui]

If I try to Hide/Show/Enable/Disable a parameter based on the null value of another, the console throw a warning like this:
Invalid comparison input: source:UnityEngine.GameObject, target:, method:Equal.

The code that originated this log message is this:

using UnityEngine;

public class testScript : MonoBehaviour
{
    public GameObject var1;
    [ShowIf(nameof(var1), null)]
    public string var2;
}

I tried on a clean project with the same Unity version (2018.4.24f1), but the issue remains.
Let me know if it is an unsurpassable structural thing.

[arimger]

Try "false". UnityEngine.Object has an overload for the bool operator to indicate if the native object exist.

[Vacui]

It works, thx really much for your help.