How do I test if a field has a value in twig? I am writing a template and if 2 fields, one of which is required the other is not.  I would like to display the one thats not required if has been filled out by the user.

I have tried numerous things 

{% if content.not_required %}
 {{ content.not_required }}
{%else%}
  {{ content.required }}

{% if content.not_required  is null %}
 {{ content.required }}  
{%else%}
  {{ content.required }}  

{% if content.not_required  == false %}
 {{ content.required }}
{%else%}
  {{ content.required }}

{% if content.not_required  == null %}
 {{ content.required }}
{%else%}
  {{ content.required }}

{% if not  content.not_required %}
 {{ content.required }}
{%else%}
  {{ content.required }}


all of these display all stories the same whether or not content.not_required was filled in.

Is there a way to do this in twig or do I need to set up some variable in a preprocess function?
There is an issue about this on Drupal.org: Checking for empty fields in Twig templates is complicated.

Use the following syntax and keep an eye on updates: 

{% if content.not_required|render %}
    {{ content.not_required }}
{% else %}
    {{ content.required }}
{% endif %}