[backend][experimentmodel] Fix DatasetBlock output handling

Fixes #268
4 jobs for 268_fix_datasetblock_missing_output_handling in 10 minutes and 22 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Build
passed build_linux_36 #201042
docker

00:10:05

90.0%
passed build_linux_37 #201043
docker

00:09:45

90.0%
passed build_macosx_36 #201040
macosx

00:10:18

90.0%
passed build_macosx_37 #201041
macosx

00:10:02

90.0%