HPCC-11548 Activity Graph Column Displays null-null

Fixes HPCC-11548

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>
Merge pull request #5960 from GordonSmith/HPCC-11548

HPCC-11548 Activity Graph Column Displays null-null

Reviewed-By: Miguel Vazquez <miguel.vazquez@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>