EDMCS Lookupset expression for custom validation

Summary:

I need to code a custom validation for a property which uses a lookupset. The main goal is to validate a property if its value is not present in the lookup set. I've tried something like :

if (lookupSets.REFERENTIEL.find(node.properties.Core.Name, false).equals("-1"))
{
return true
} else
{
return false
}

I'm note sure at all of the syntaxe to use to exploit the find() method.. I've tried with equals() method to check if the value is found but it doesn't work.

Could you help me or give a documentation for the usage of find() method ?

Thx

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