NMS-6836: Add null protection in EventLabelComparator
[bamboo] Automated branch merge (from 1.12:96db1cb80a1e24088fc33b2d602828efb69762c1)
[bamboo] Automated branch merge (from rc/stable/1.14.0:1e6a32afa85230e04d11e9b5b055a15190007f4c)