The correct formula is:

IF(

NOT(ISBLANK(Nickname__c)),

Nickname__c,

FirstName

)

Salesforce recommends ISBLANK() to check whether a field has no value, including text fields. Since Nickname__c is optional, the formula first checks whether it is not blank. If it has a value, Salesforce uses the nickname. If it is blank, Salesforce uses FirstName .

A is incorrect because BLANKVALUE() is not used this way inside NOT() .

B is incorrect because the logic is reversed and ISNULL() is not preferred for text fields.

D is incorrect because TEXT() is not needed for a text field and does not perform a blank check.

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