Make consumes call check if edm::InputTag is empty

[Dr15Jones]

Previously, passing an empty edm::InputTag to consumes would make the framework think you did a consumesMany (since internally an empty tag is used for that purpose). This change makes an empty tag passed to consumes behave the same way as if you had a tag for a non-existent label.

[cmsbuild]

A new Pull Request was created by @Dr15Jones (Chris Jones) for CMSSW_7_1_X.

Make consumes call check if edm::InputTag is empty

It involves the following packages:

FWCore/Framework

@cmsbuild, @Degano, @Dr15Jones, @ktf, @nclopezo can you please review it and eventually sign? Thanks.
@wmtan this is something you requested to watch as well.
You can sign-off by replying to this message having '+1' in the first line of your reply.
You can reject by replying to this message having '-1' in the first line of your reply.
@ktf you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[Dr15Jones]

@ktf Giulio, do you want this backported to 7_0_X to support #1988 ?

[Dr15Jones]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_1_X IBs unless changes or unless it breaks tests. @ktf can you please take care of it?

[ktf]

Do we care anymore about consumes in 70X, since it's not gonna be multithreaded in any case?

@davidlange6

[Dr15Jones]

I only asked because the pull request which found the bug is set for 7_0. However the bug does affect single threaded as well.

[cmsbuild]

+1
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-2142/40/summary.html

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_1_X IBs unless changes (tests are also fine). @ktf can you please take care of it?