Variant table &1 contains empty cells in line &2

What causes this issue?

The variant table has empty cells.

System Response

Empty cells in variant tables have an evident negative impact on the
performance. See also note 917987. Such empty fields should generally be
avoided.

How to fix this error?

Correct the entries of the variant table in the classical transaction
(CU60). (In PMEVC, it is not possible to maintain variant table content
with empty cells.)

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.