Total of two separate AVERAGEIF formulas

Hi all,
I have two columns each returning averageifs formulas of data on a different sheet.

An example of this formula is:
=IFERROR(AVERAGEIFS('Data Sheet'!D:D,'Data Sheet'!A:A,'Main Sheet'!B8),"")

These work fine, no issues however, I want a third column that gives the sum of these two averages.

I try using a simple =IFERROR((A1+B1),"") formula, but I only get a result when there is a figure in BOTH columns.
If I use a basic =A+B, I get #VALUE! unless both cells contain data.

Is there a way to count both, regardless of whether there is data in both cells?

Thanks!

=sum(a1:b1)

Perhaps

YES! Thank you davsth
This is the fix!