Hi @wu cong? , thank you for your question.
Trifacta differentiates between an empty value (meaning the field is simply empty) and a null value:
Indeed, to identify a null value, you can use the function ISNULL()
To identify a value that is either empty or null, you can use the function ISMISSING()
To identify an empty value, you can use equality, like PHONE_NUMBER=="" . Meaning - is an empty string.
In the picture above, I'm using the "case-custom condition" transform to add multiple cases, as per your scenario.
You can change the fields to what your goal is.
I've used the ISMISSING() function in the 2nd condition because conditions' order in a case condition takes precedence. So if the first condition wasn't met, it means the ISMISSING() will only find empty values, not null values.
I hope that makes sense.
Feel free to ask any further questions.
Thanks,
Amit.