Missing

Missing[] represents data that is missing.

Missing["reason"] specifies a reason for the data being missing.

Missing["reason", expr] associates the expression expr with the missing data.

Examples

Create missing data:

Missing["NotAvailable"]
(* Missing["NotAvailable"] *)

Missing values propagate through computations:

{1, 2, Missing[], 4} + 1
(* {2, 3, Missing[], 5} *)

Please visit the official Wolfram Language Reference for more details.