Fix associationMapFilterValues() for empty input AssociationMap

[makortel]

Fixes the invalid reference exception from MultiTrackValidator in wfs 500207.0, 250207.0.

Tested in CMSSW_7_5_X_2015-05-07-1100 with limited matrix + wfs 500207.0, 250207.0. No changes expected in results.

[cmsbuild]

A new Pull Request was created by @makortel (Matti Kortelainen) for CMSSW_7_5_X.

Fix associationMapFilterValues() for empty input AssociationMap

It involves the following packages:

CommonTools/Utils

@nclopezo, @cvuosalo, @monttj, @cmsbuild, @slava77, @vadler can you please review it and eventually sign? Thanks.
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[slava77]

@cmsbuild please test

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

+1
Tested at: 600394f
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-9000/47/summary.html

[cvuosalo]

+1

For #9000 600394f

Small bug fix for an exception from associationMapFilterValues(). It should not change monitored physics quantities.

The code change is satisfactory, and Jenkins tests against baseline CMSSW_7_5_X_2015-05-07-2300 show no significant differences, as expected.

[makortel]

ping

[davidlange6]

bypassing a clear fix