Boolean operator with objects

[tobiascapin]

Hello, I'm migrating my templates from another java library derived from Twig syntax.
I have some troubles with implicit boolean expressions, I cannot understand very well why this expression works:

{% if myobj %}

and why this doesn't work

{% if not myobj %}

I know it can be replaced by {% if myobj is empty %} but since the first works, make it sense to not use the "not"?