I want to show records where a date-field is either blank or date is more than today

OpenAI suggested this:
OR([ExpectedDeliveryDate] IS NULL, [ExpectedDeliveryDate] > CURRENT_DATE())
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I also tried this:
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This works, but I need to consider NULL:
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So the question is ;
Why does this not work and what should I use instead?
OR([ExpectedDeliveryDate] IS NULL, [ExpectedDeliveryDate] > CURRENT_DATE())

Have a look at List of expressions and Custom expressions, it will help you grasp the concept of Custom Expressions