Fixed bug which was crashing ROOT in fitting empty histograms

[dinardo]

PR description:

I fixed a bug that was crashing ROOT: the application was trying to fit empty histograms.
Now I've protected the fit by checking whether the histogram is empty or not

PR validation:

Now the crash should not occur anymore

if this PR is a backport please specify the original PR and why you need to backport that PR:

#35903

[cmsbuild]

A new Pull Request was created by @dinardo (Mauro) for CMSSW_12_0_X.

It involves the following packages:

• DQM/BeamMonitor (dqm)
• DQM/Integration (dqm)

@emanueleusai, @ahmad3213, @cmsbuild, @jfernan2, @pmandrik, @pbo0, @rvenditti can you please review it and eventually sign? Thanks.
@battibass, @threus, @batinkov, @francescobrivio this is something you requested to watch as well.
@perrotta, @dpiparo, @qliphy you are the release manager for this.

cms-bot commands are listed here

• Backported from Fixed bug which was crashing ROOT in fitting empty histograms #35903

[francescobrivio]

backport of #35903

[francescobrivio]

@cmsbuild please test

[cmsbuild]

+1

Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-16d2ee/20063/summary.html
COMMIT: 4968ad9
CMSSW: CMSSW_12_0_X_2021-10-29-1100/slc7_amd64_gcc900
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week0/cms-sw/cmssw/35908/20063/install.sh to create a dev area with all the needed externals and cmssw changes.

Comparison Summary

Summary:

• No significant changes to the logs found
• Reco comparison results: 0 differences found in the comparisons
• DQMHistoTests: Total files compared: 39
• DQMHistoTests: Total histograms compared: 2998564
• DQMHistoTests: Total failures: 0
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 2998542
• DQMHistoTests: Total skipped: 22
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 38 files compared)
• Checked 165 log files, 37 edm output root files, 39 DQM output files
• TriggerResults: no differences found

[jfernan2]

@dinardo @francescobrivio I am not sure if this bug was detected in Online (and I missed it) but I understand we whould integrate it in current data taking, right?

[jfernan2]

+1
Tested in Online DQM at P5

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_12_0_X IBs (tests are also fine) and once validation in the development release cycle CMSSW_12_2_X is complete. This pull request will now be reviewed by the release team before it's merged. @perrotta, @dpiparo, @qliphy (and backports should be raised in the release meeting by the corresponding L2)

[perrotta]

+1

• Ok for the backport