This originally came up during the test logs when building cryostat on top of jmc-core 9.0.0, but we can see a handful of instances of:

2024-01-22 10:19:38,997 WARNING [org.ope.jmc.fli.configuration] (executor-thread-1) Couldn't find constraint for null

Taking a bit of a deeper look, this happens when EventTypeMetadataV2 is determining the contentType, and is jdk.settings.Throttle. When passed into CommonConstraints.forContentTypeV2(), the constraint falls through to the null option and emits this logger warning before returning UnitLookup.PLAIN_TEXT