Unknown error in fronttail

I get the following error. Any idea where I could look?

2021-02-24 11:20:05.251 [ERROR] [xt.xbase.jvmmodel.JvmModelAssociator] - Error calling inferrer

java.lang.NullPointerException: null

at org.openhab.core.model.rule.jvmmodel.RulesJvmModelInferrer.lambda$2(RulesJvmModelInferrer.java:121) ~[?:?]

at org.eclipse.xtext.xbase.lib.ObjectExtensions.operator_doubleArrow(ObjectExtensions.java:140) ~[?:?]

at org.openhab.core.model.rule.jvmmodel.RulesJvmModelInferrer.lambda$1(RulesJvmModelInferrer.java:127) ~[?:?]

at org.eclipse.xtext.xbase.lib.internal.FunctionDelegate.apply(FunctionDelegate.java:43) ~[?:?]

at com.google.common.collect.Lists$TransformingRandomAccessList$1.transform(Lists.java:612) ~[bundleFile:?]

at com.google.common.collect.TransformedIterator.next(TransformedIterator.java:47) ~[bundleFile:?]

at org.eclipse.xtext.xbase.jvmmodel.JvmTypesBuilder.operator_add(JvmTypesBuilder.java:138) ~[bundleFile:?]

at org.openhab.core.model.rule.jvmmodel.RulesJvmModelInferrer.lambda$0(RulesJvmModelInferrer.java:130) ~[?:?]

at org.eclipse.xtext.xbase.jvmmodel.JvmModelAssociator$1.run(JvmModelAssociator.java:398) [bundleFile:?]

at org.eclipse.xtext.xbase.jvmmodel.JvmModelAssociator.installDerivedState(JvmModelAssociator.java:408) [bundleFile:?]

at org.eclipse.xtext.resource.DerivedStateAwareResource.installDerivedState(DerivedStateAwareResource.java:244) [bundleFile:?]

at org.eclipse.xtext.xbase.resource.BatchLinkableResource.getContents(BatchLinkableResource.java:149) [bundleFile:?]

at org.eclipse.xtext.build.IncrementalBuilder$InternalStatefulIncrementalBuilder.lambda$launch$2(IncrementalBuilder.java:265) [bundleFile:?]

at com.google.common.collect.Iterators$6.transform(Iterators.java:783) [bundleFile:?]

at com.google.common.collect.TransformedIterator.next(TransformedIterator.java:47) [bundleFile:?]

at com.google.common.collect.FluentIterable.copyInto(FluentIterable.java:791) [bundleFile:?]

at org.eclipse.xtext.build.ClusteringStorageAwareResourceLoader.executeClustered(ClusteringStorageAwareResourceLoader.java:69) [bundleFile:?]

at org.eclipse.xtext.build.BuildContext.executeClustered(BuildContext.java:55) [bundleFile:?]

at org.eclipse.xtext.build.IncrementalBuilder$InternalStatefulIncrementalBuilder.launch(IncrementalBuilder.java:259) [bundleFile:?]

at org.eclipse.xtext.build.IncrementalBuilder.build(IncrementalBuilder.java:404) [bundleFile:?]

at org.eclipse.xtext.build.IncrementalBuilder.build(IncrementalBuilder.java:386) [bundleFile:?]

at org.eclipse.xtext.ide.server.ProjectManager.doBuild(ProjectManager.java:106) [bundleFile:?]

at org.eclipse.xtext.ide.server.BuildManager.internalBuild(BuildManager.java:190) [bundleFile:?]

at org.eclipse.xtext.ide.server.WorkspaceManager.lambda$didChangeFiles$4(WorkspaceManager.java:279) [bundleFile:?]

at org.eclipse.xtext.ide.server.LanguageServerImpl.lambda$runBuildable$15(LanguageServerImpl.java:453) [bundleFile:?]

at org.eclipse.xtext.ide.server.concurrent.WriteRequest.run(WriteRequest.java:52) [bundleFile:?]

at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515) [?:?]

at java.util.concurrent.FutureTask.run(FutureTask.java:264) [?:?]

at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) [?:?]

at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) [?:?]

at java.lang.Thread.run(Thread.java:834) [?:?]

It looks like it is related to a DSL rule. Can’t say much more than that though…

I found an item in an if statement, where the .state was missing. It seams that this was the problem.
I wound why this error was not described more specific!

I think the real problem was a switch group (ON when all are ON) where I accidently added a temperature item. This was hard to find.