Prometheus plugins exception in log results in empty page when scraping

Hello,

Steps to reproduce

Use prometheus-plugin: 2.0.8 and Jenkins: 2.235.3 with a large number of jobs and scrape them, an empty scraping page will be returned

Expected behaviour Show the scraped output on the /prometheus endpoint

Actual behaviour When navigating to the webpage/prometheus, I am receiving an empty page with a 200 status code. In my logs I see:

A thread (prometheus_async_worker thread/767) died unexpectedly due to an uncaught exception, this may leave your Jenkins in a bad way and is usually indicative of a bug in the code.
java.lang.NullPointerException
	at org.jenkinsci.plugins.prometheus.JobCollector.lambda$appendJobMetrics$1(JobCollector.java:310)
	at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)
	at java.util.HashMap$EntrySpliterator.forEachRemaining(HashMap.java:1699)
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)
	at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:566)
	at org.jenkinsci.plugins.prometheus.JobCollector.appendJobMetrics(JobCollector.java:310)
	at org.jenkinsci.plugins.prometheus.JobCollector.lambda$collect$0(JobCollector.java:220)
	at org.jenkinsci.plugins.prometheus.util.Jobs.forEachJob(Jobs.java:14)
	at org.jenkinsci.plugins.prometheus.JobCollector.collect(JobCollector.java:214)
	at io.prometheus.client.CollectorRegistry$MetricFamilySamplesEnumeration.findNextElement(CollectorRegistry.java:190)
	at io.prometheus.client.CollectorRegistry$MetricFamilySamplesEnumeration.nextElement(CollectorRegistry.java:223)
	at io.prometheus.client.CollectorRegistry$MetricFamilySamplesEnumeration.nextElement(CollectorRegistry.java:144)
	at io.prometheus.client.exporter.common.TextFormat.write004(TextFormat.java:22)
	at org.jenkinsci.plugins.prometheus.service.DefaultPrometheusMetrics.collectMetrics(DefaultPrometheusMetrics.java:51)
	at org.jenkinsci.plugins.prometheus.service.PrometheusAsyncWorker.execute(PrometheusAsyncWorker.java:41)
	at hudson.model.AsyncPeriodicWork.lambda$doRun$0(AsyncPeriodicWork.java:100)
	at java.lang.Thread.run(Thread.java:748)

I am also seeing

A thread (prometheus_async_worker thread/1054) died unexpectedly due to an uncaught exception, this may leave your Jenkins in a bad way and is usually indicative of a bug in the code.
java.lang.NullPointerException

In the prometheus logs, it seems to still receive information correctly from jobs, but I got no output when jenkins is scraped.

Server configuration prometheus-plugin: 2.0.8 Jenkins: 2.235.3

Settings for the plugins is the default settings.

Notify @markyjackson-taulia

[olafrauch]

Similar issue here. Since plugin 2.0.8 upgrade: There is a ClassCastException in the log and the /prometheus page is empty

SEVERE h.i.i.InstallUncaughtExceptionHandler$DefaultUncaughtExceptionHandler#uncaughtException: A thread (prometheus_async_worker thread/3301139) died unexpectedly due to an uncaught exception, this may leave your Jenkins in a bad way and is usually indicative of a bug in the code. java.lang.ClassCastException

Note: As soon as I disable the five “Count Duration *” settings of the plugin in “Manage Jenkins”, the error log entry is gone and the (now less) metrics are back.

[github-actions[bot]]

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