How can I create a custom calculation that will not error when adding NULL values?

Hi,

Version: BI 4.0 SP8.3

Database: Microsoft SQL Server 2012 Analysis Services

Question: How can I create a custom calculation that will not produce the following error when adding a NULL value?

I am getting this error:

The MDAS service encountered an error.

Failed to get representation: RuntimeException occurred : com.sap.ip.bi.bics.exceptions.BicsProgrammErrorException: Invalid program status: Invalid new element, level to low: 1 but expected 2

I believe the error is occurring due to the Total Expenses custom calculation (see red arrow below):

Total Expenses is simply adding the values from the other custom calculations above it (see blue arrows above).

The formula is: 'FORMULA/[Activity]/Formula1' + 'FORMULA/[Activity]/Formula4' + 'FORMULA/[Activity]/Formula6'

This formula works great when all three calculations have values. The problem arises when one of them has a NULL value.

How can I create a custom calculation that will not fail when adding NULL values?

Thanks,

Michael