HI David
A question best put to the developer forum but my thinking is this is because null, in the context of your response JSON is not actually a "value" - this is appearing to the Data Action, and anything that would use it as no value rather than a value of "null". You might want to look at setting default values for things where you may get a null/no value back, or potentially look at the code/service that provides the API you're calling to see if the response can be modified on that side.
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Vaun McCarthy
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