___________ returns either the non-null result of the first expression.
A. $Null
B. $ifNull
C. $ElseNull
D. None of the mentioned
Answer:A
___________ returns either the non-null result of the first expression.
A. $Null B. $ifNull C. $ElseNull D. None of the mentioned
Explanation:$ifNull returns the result of the second expression if the first expression results in a null result. 10.__________ take as input a single expression, evaluating the expression once for each input document, and maintain their state for the group of documents.