The IsOperative transformation and a number of others need to check their prerequisites before being created, like the Time Offset transformation. In the case of IsOperative, it needs to check if there are any date fields present. If there aren't it presents a UI with nothing in its dropdowns.
The Relational String priority transformation doesn't enforce the values on the string priority drop down, and the multivalue union transformation doesn't enforce the left or right field drop downs.
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