Allow Boolean Conditions.
The Condition in the designer needs a Object Name, Relationship and a Value. When the value in the JSON is a boolean, then the expression can't be set in de designer.
Just a simple "if (value)" can't be set, should be "if (value == true)" but that can't be set.
Can be done in de Advanced mode like this:
The Relationship list should be extended with "Is True" and "Is False' and then the Value field can be empty.