Mandatory input missing in row &1/column &2

What causes this issue?

In row &v1& of the decision table, no value has been predefined for
column &v2& against which input data should be compared. However, this
column has been flagged as 'input mandatory'.

System Response

The decision table cannot be activated.

How to fix this error?

Proceed as follows to solve the problem:
If a value is required in column &v2& for the decision table to
calculate a result, enter the missing value.
If a value is not required, remove the 'mandatory' flag for the column.

Procedure for System Administrators

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Error message extract from SAP system. Copyright SAP SE.