Discovery stopped at the very beginning stage and it stopped automatically and throwing "java.lang.NullPointerException" exception in Discovery log and Mid server Agent Log.

Below error is the error reference.

java.lang.NullPointerException
at com.service_now.mid.creds.provider.standard.StandardCredentialsProvider.iterator(StandardCredentialsProvider.java:156)
at com.service_now.mid.probe.shazzam.scanners.SNMP.getCredsIterator(SNMP.java:383)
at com.service_now.mid.probe.shazzam.scanners.SNMP.sendSpamTaps(SNMP.java:283)
at com.service_now.mid.probe.shazzam.scanners.SNMP.sendFirstTap(SNMP.java:252)
at com.service_now.mid.probe.shazzam.scanners.SNMP.nextPhase(SNMP.java:199)
at com.service_now.mid.probe.shazzam.PortScannerEngine.run(PortScannerEngine.java:69)
at com.service_now.mid.probe.Shazzam.processChunk(Shazzam.java:166)
at com.service_now.mid.probe.ShazzamBase.syncProcessChunk(ShazzamBase.java:67)
at com.service_now.mid.probe.Shazzam.probe(Shazzam.java:136)
at com.service_now.mid.probe.AProbe.process(AProbe.java:103)
at com.service_now.mid.queue_worker.AWorker.runWorker(AWorker.java:122)
at com.service_now.mid.queue_worker.AWorkerThread.run(AWorkerThread.java:20)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)

If the Midserver is not set to work in Global Domain, then we to need always set the multi domain properties value set as "False".

Below SerrvieNow documentation to refer how to set your Midserver to work in Global Domain and can explore targets in other domains.

Configure a multi-domain MID Server

With this property set to false, we cannot use a MID Server in the global domain to explore targets in other domains. For some reason, the MID Server Property "mid.enable_multidomain_mid" when set to true is causing a NullPointerException in customer instance when Discovery run and it stops at the very beginning level, without triggering and probes or patterns. When it set to false, credential syncing works correctly and so does Discovery.

Steps to Follow:-

1. Navigate to Midserver from Instance Navigator.
2. Need to select the properties
3. Now search "mid.enable_multidomain_mid" in Name search bar.
4. Change the value to "False" if your Midserver is not working as Global domain.
   
5. Below the screenshot for reference how to set this property to false.