Error in generating State Diagram

[novr]

Describe the bug
test.puml

@startuml test
state S.I {
    S.I --> S.I
}
@enduml

To Reproduce

1. java -jar plantuml-1.2023.4.jar test.puml
2. See error

Error java.lang.NullPointerException: Cannot invoke "net.sourceforge.plantuml.abel.Entity.getGroupType()" because the return value of "net.sourceforge.plantuml.abel.Entity.getParentContainer()" is null
java.lang.NullPointerException: Cannot invoke "net.sourceforge.plantuml.abel.Entity.getGroupType()" because the return value of "net.sourceforge.plantuml.abel.Entity.getParentContainer()" is null
at net.sourceforge.plantuml.statediagram.StateDiagram.checkConcurrentStateOkInternal(StateDiagram.java:74)
at net.sourceforge.plantuml.statediagram.StateDiagram.checkConcurrentStateOk(StateDiagram.java:61)
at net.sourceforge.plantuml.statediagram.command.CommandLinkStateCommon.getEntity(CommandLinkStateCommon.java:180)
at net.sourceforge.plantuml.statediagram.command.CommandLinkStateCommon.getEntityEnd(CommandLinkStateCommon.java:152)
at net.sourceforge.plantuml.statediagram.command.CommandLinkStateCommon.executeArg(CommandLinkStateCommon.java:83)
at net.sourceforge.plantuml.statediagram.command.CommandLinkStateCommon.executeArg(CommandLinkStateCommon.java:60)
at net.sourceforge.plantuml.command.SingleLineCommand2.execute(SingleLineCommand2.java:150)
at net.sourceforge.plantuml.command.ProtectedCommand.execute(ProtectedCommand.java:57)
at net.sourceforge.plantuml.AbstractPSystem.executeCommand(AbstractPSystem.java:177)
at net.sourceforge.plantuml.command.PSystemCommandFactory.executeFewLines(PSystemCommandFactory.java:125)
at net.sourceforge.plantuml.command.PSystemCommandFactory.createSystem(PSystemCommandFactory.java:108)
at net.sourceforge.plantuml.PSystemBuilder.createPSystem(PSystemBuilder.java:146)
at net.sourceforge.plantuml.BlockUml.getDiagram(BlockUml.java:188)
at net.sourceforge.plantuml.SourceFileReaderAbstract.getGeneratedImages(SourceFileReaderAbstract.java:171)
at net.sourceforge.plantuml.Run.manageFileInternal(Run.java:525)
at net.sourceforge.plantuml.Run.processArgs(Run.java:408)
at net.sourceforge.plantuml.Run.manageAllFiles(Run.java:375)
at net.sourceforge.plantuml.Run.main(Run.java:209)
You should send a mail to plantuml@gmail.com or post to https://plantuml.com/qa with this log (V1.2023.3)
Error line 4 in file: test.puml
Some diagram description contains errors

Expected behavior

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: macOS 12.6.3 (21G419)
• java -version

java version "18.0.1.1" 2022-04-22
Java(TM) SE Runtime Environment (build 18.0.1.1+2-6)
Java HotSpot(TM) 64-Bit Server VM (build 18.0.1.1+2-6, mixed mode, sharing)

Additional context

This error does not occur with plantuml-1.2023.1.jar.
The error occurs from plantuml-1.2023.2.jar or later.