MSPileup monitoringTask fail to track containers without any wmcore_transferor rules

[amaltaro]

Impact of the bug
MSPileup

Describe the bug
Hasan pointed out to this RelVal pileup:

/RelValMinBias_14TeV/CMSSW_13_1_0_pre2-131X_mcRun4_realistic_v2_2026D95noPU-v2/GEN-SIM

which is supposed to have 1 wmcore_transferor rule locking it at T2_CH_CERN, accessible through (but also copied in [1]):
https://cmsweb.cern.ch/ms-pileup/data/pileup?pileupName=/RelValMinBias_14TeV/CMSSW_13_1_0_pre2-131X_mcRun4_realistic_v2_2026D95noPU-v2/GEN-SIM

It turns out that that rule 4650a485fe3f44258f5aedb60139a5cb does not even exist in Rucio; and MSPileup is not taking any action on the pileup either.

Problem seems to be in the monitoringTask which iterates through all the wmcore_transferor, however, it does not account for the case where no rules are found in Rucio:
https://github.com/dmwm/WMCore/blob/master/src/python/WMCore/MicroService/MSPileup/MSPileupTasks.py#L259

How to reproduce it
Have a pileup configuration with existent rules, then delete all wmcore_transferor rules.

Expected behavior
If a pileup is active (active=True), it has expected RSEs in the configuration, but no rules in Rucio are found; it is expected that MSPileup will:

• cleanup the currentRSEs property
• and cleanup the ruleIds property.

With that, the activeTask will pick it up and make the relevant data placement.

Additional context and error message
[1]

{"result": [
 {
  "pileupName": "/RelValMinBias_14TeV/CMSSW_13_1_0_pre2-131X_mcRun4_realistic_v2_2026D95noPU-v2/GEN-SIM",
  "pileupType": "premix",
  "insertTime": 1681914426,
  "lastUpdateTime": 1682596591,
  "expectedRSEs": [
    "T2_CH_CERN"
  ],
  "currentRSEs": [
    "T2_CH_CERN"
  ],
  "fullReplicas": 1,
  "campaigns": [],
  "containerFraction": 1.0,
  "replicationGrouping": "ALL",
  "activatedOn": 1682596591,
  "deactivatedOn": 1681914426,
  "active": true,
  "pileupSize": 33060714720,
  "ruleIds": [
    "4650a485fe3f44258f5aedb60139a5cb"
  ]
}]}