How to properly use if not statement with twig - twig

Question

I have been trying to figure out how to use the if not clause with Twig template engine.
According to the documents:
You can also use not to check for values that evaluate to false:
So I'm trying to use it like this:
{% if not signed_in %}
You are not signed in.
{% endif %}
And signed_in comes from a middleware. Looking like this:
if (!$this->container->auth->check()) {
/* Render a Sign-up */
return $this->container->view->render($response, 'subscriber/index.twig', ['signed_in' => false]);
}
So if I {{ dump(signed_in) }} when I'm not signed in it returns false. But when I'm signed in, singed_in returns null.
The current solution I'm going with is {% if signed_in is defined %}, but that is actually not what I'm looking for, or is it?

Answer 1

Twig != is a comparison operator.
The following comparison operators are supported in any expression: ==, !=, <, >, >=, and <=
You can use != to compare any two things that php lets you compare, and what you get back is a boolean.
Twig not is a logic operator. (so are and and or)
not: Negates a statement.

Answer 2

I recommend you to use:
{% if signed_in == true %} or {% if signed_in == false%}
This is the twig comportment:
{% set testTrue = true %}
{% set testFalse = false %}
{% set testNull = null %}
{% set testString = "something" %}
{% if testTrue %} {# true #}
{% if testFalse %}{# false#}
{% if testNull %} {# false#}
{% if testString %} {# true #}
{% if not testTrue %}{# false#}
{% if not testFalse %}{# true#}
{% if not testNull %} {# false !!!!!!!!!!!!!!!! #}
{% if not testString %} {# false#}
{% if testTrue == true %} {# true #}
{% if testFalse == true %} {# false#}
{% if testNull == true %} {# false#}
{% if testString == true %} {# true #}
{% if not testTrue == true %} {# false#}
{% if not testFalse == true %} {# true #}
{% if not testNull == true %} {# true #}
{% if not testString == true %} {# false#}
other tests good to know
{% if testTrue == 1 %} {# true #}
{% if testFalse == 1 %} {# false#}
{% if testTrue == "1" %} {# true #}
{% if testFalse == "1" %} {# false#}