AD B2C - Custom Policies - Evaluate custom extension

Thank you for the responses, but general links to documentation is not what I needed, and the solution seems not to be included there.  

I need to understand (in detail because the documentation only get halfway) on how to evauate boolean values. 

The issue is that the snippet below are execuyting even for users that do NOT have the attribute at all. The boolean can be either not set, false or true. I only want to run my techincal profile when the atttribute exists and is set to true. 

  <Precondition Type="ClaimEquals" ExecuteActionsIf="false">

                            <Value>extension_AlwaysMFA</Value>

                            <Value>True</Value>

                            <Action>SkipThisOrchestrationStep</Action>

 </Precondition>


In languages like Typescript for example i would simply type:

if (extension_AlwaysMFA) triggerMfa();

But how do I evaluate the boolean using custom policies if it can be unset as well?