Realm, initializing an empty string array returns "Unsupported type java.lang.String[]" on build

Question

I'm trying to initialize an empty string array in a Kotlin class, however the syntax for this appears to be escaping me, I've checked the Kotlin docs and I think I'm doing it in the correct way however I always end up with the following message when it builds:

Error:Execution failed for task ':core:compileDebugJavaWithJavac'.
> java.lang.IllegalStateException: Unsupported type java.lang.String[]

I've tried the following methods of initializing it, Android Studio doesn't red line any of these.

var categories = emptyArray<String>()
var categories = arrayOf<String>()
var categories: Array<String> = emptyArray()
var categories: Array<String> = arrayOf()

It does appear to be a bug, interestingly enough it's affecting my previously stable Kotlin setup on AS 2.3.2, and again strangely, I get the same build error when trying to create String Lists.

So it seems to be a bug specifically on my laptop, I'm running exact same code on my desktop using the same version of AS, on the same project, everything identical, and yet it compiles.

Alright the bug is now affecting my desktop where I'm using regular Java, not even Kotlin, here's the gradle stacktrace:

Exception is:
org.gradle.api.tasks.TaskExecutionException: Execution failed for task ':core:compileDebugJavaWithJavac'.
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:84)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:55)
    at org.gradle.api.internal.tasks.execution.SkipUpToDateTaskExecuter.execute(SkipUpToDateTaskExecuter.java:62)
    at org.gradle.api.internal.tasks.execution.ValidatingTaskExecuter.execute(ValidatingTaskExecuter.java:58)
    at org.gradle.api.internal.tasks.execution.SkipEmptySourceFilesTaskExecuter.execute(SkipEmptySourceFilesTaskExecuter.java:88)
    at org.gradle.api.internal.tasks.execution.ResolveTaskArtifactStateTaskExecuter.execute(ResolveTaskArtifactStateTaskExecuter.java:46)
    at org.gradle.api.internal.tasks.execution.SkipTaskWithNoActionsExecuter.execute(SkipTaskWithNoActionsExecuter.java:51)
    at org.gradle.api.internal.tasks.execution.SkipOnlyIfTaskExecuter.execute(SkipOnlyIfTaskExecuter.java:54)
    at org.gradle.api.internal.tasks.execution.ExecuteAtMostOnceTaskExecuter.execute(ExecuteAtMostOnceTaskExecuter.java:43)
    at org.gradle.api.internal.tasks.execution.CatchExceptionTaskExecuter.execute(CatchExceptionTaskExecuter.java:34)
    at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter$EventFiringTaskWorker$1.execute(DefaultTaskGraphExecuter.java:236)
    at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter$EventFiringTaskWorker$1.execute(DefaultTaskGraphExecuter.java:228)
    at org.gradle.internal.Transformers$4.transform(Transformers.java:169)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:106)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:61)
    at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter$EventFiringTaskWorker.execute(DefaultTaskGraphExecuter.java:228)
    at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter$EventFiringTaskWorker.execute(DefaultTaskGraphExecuter.java:215)
    at org.gradle.execution.taskgraph.AbstractTaskPlanExecutor$TaskExecutorWorker.processTask(AbstractTaskPlanExecutor.java:77)
    at org.gradle.execution.taskgraph.AbstractTaskPlanExecutor$TaskExecutorWorker.run(AbstractTaskPlanExecutor.java:58)
    at org.gradle.execution.taskgraph.DefaultTaskPlanExecutor.process(DefaultTaskPlanExecutor.java:32)
    at org.gradle.execution.taskgraph.DefaultTaskGraphExecuter.execute(DefaultTaskGraphExecuter.java:113)
    at org.gradle.execution.SelectedTaskExecutionAction.execute(SelectedTaskExecutionAction.java:37)
    at org.gradle.execution.DefaultBuildExecuter.execute(DefaultBuildExecuter.java:37)
    at org.gradle.execution.DefaultBuildExecuter.access$000(DefaultBuildExecuter.java:23)
    at org.gradle.execution.DefaultBuildExecuter$1.proceed(DefaultBuildExecuter.java:43)
    at org.gradle.execution.DryRunBuildExecutionAction.execute(DryRunBuildExecutionAction.java:32)
    at org.gradle.execution.DefaultBuildExecuter.execute(DefaultBuildExecuter.java:37)
    at org.gradle.execution.DefaultBuildExecuter.execute(DefaultBuildExecuter.java:30)
    at org.gradle.initialization.DefaultGradleLauncher$3.execute(DefaultGradleLauncher.java:196)
    at org.gradle.initialization.DefaultGradleLauncher$3.execute(DefaultGradleLauncher.java:193)
    at org.gradle.internal.Transformers$4.transform(Transformers.java:169)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:106)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:56)
    at org.gradle.initialization.DefaultGradleLauncher.doBuildStages(DefaultGradleLauncher.java:193)
    at org.gradle.initialization.DefaultGradleLauncher.doBuild(DefaultGradleLauncher.java:119)
    at org.gradle.initialization.DefaultGradleLauncher.run(DefaultGradleLauncher.java:102)
    at org.gradle.launcher.exec.GradleBuildController.run(GradleBuildController.java:71)
    at org.gradle.tooling.internal.provider.runner.BuildModelActionRunner.run(BuildModelActionRunner.java:50)
    at org.gradle.launcher.exec.ChainingBuildActionRunner.run(ChainingBuildActionRunner.java:35)
    at org.gradle.tooling.internal.provider.runner.RunAsBuildOperationBuildActionRunner$1.execute(RunAsBuildOperationBuildActionRunner.java:43)
    at org.gradle.tooling.internal.provider.runner.RunAsBuildOperationBuildActionRunner$1.execute(RunAsBuildOperationBuildActionRunner.java:40)
    at org.gradle.internal.Transformers$4.transform(Transformers.java:169)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:106)
    at org.gradle.internal.progress.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:56)
    at org.gradle.tooling.internal.provider.runner.RunAsBuildOperationBuildActionRunner.run(RunAsBuildOperationBuildActionRunner.java:40)
    at org.gradle.tooling.internal.provider.runner.SubscribableBuildActionRunner.run(SubscribableBuildActionRunner.java:75)
    at org.gradle.launcher.exec.ChainingBuildActionRunner.run(ChainingBuildActionRunner.java:35)
    at org.gradle.launcher.exec.InProcessBuildActionExecuter.execute(InProcessBuildActionExecuter.java:41)
    at org.gradle.launcher.exec.InProcessBuildActionExecuter.execute(InProcessBuildActionExecuter.java:26)
    at org.gradle.tooling.internal.provider.ContinuousBuildActionExecuter.execute(ContinuousBuildActionExecuter.java:75)
    at org.gradle.tooling.internal.provider.ContinuousBuildActionExecuter.execute(ContinuousBuildActionExecuter.java:49)
    at org.gradle.tooling.internal.provider.ServicesSetupBuildActionExecuter.execute(ServicesSetupBuildActionExecuter.java:44)
    at org.gradle.tooling.internal.provider.ServicesSetupBuildActionExecuter.execute(ServicesSetupBuildActionExecuter.java:29)
    at org.gradle.launcher.daemon.server.exec.ExecuteBuild.doBuild(ExecuteBuild.java:67)
    at org.gradle.launcher.daemon.server.exec.BuildCommandOnly.execute(BuildCommandOnly.java:36)
    at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120)
    at org.gradle.launcher.daemon.server.exec.WatchForDisconnection.execute(WatchForDisconnection.java:47)
    at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120)
    at org.gradle.launcher.daemon.server.exec.ResetDeprecationLogger.execute(ResetDeprecationLogger.java:26)
    at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120)
    at org.gradle.launcher.daemon.server.exec.RequestStopIfSingleUsedDaemon.execute(RequestStopIfSingleUsedDaemon.java:34)
    at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120)
    at org.gradle.launcher.daemon.server.exec.ForwardClientInput$2.call(ForwardClientInput.java:74)
    at org.gradle.launcher.daemon.server.exec.ForwardClientInput$2.call(ForwardClientInput.java:72)
    at org.gradle.util.Swapper.swap(Swapper.java:38)
    at org.gradle.launcher.daemon.server.exec.ForwardClientInput.execute(ForwardClientInput.java:72)
    at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120)
    at org.gradle.launcher.daemon.server.exec.LogAndCheckHealth.execute(LogAndCheckHealth.java:55)
    at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120)
    at org.gradle.launcher.daemon.server.exec.LogToClient.doBuild(LogToClient.java:60)
    at org.gradle.launcher.daemon.server.exec.BuildCommandOnly.execute(BuildCommandOnly.java:36)
    at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120)
    at org.gradle.launcher.daemon.server.exec.EstablishBuildEnvironment.doBuild(EstablishBuildEnvironment.java:72)
    at org.gradle.launcher.daemon.server.exec.BuildCommandOnly.execute(BuildCommandOnly.java:36)
    at org.gradle.launcher.daemon.server.api.DaemonCommandExecution.proceed(DaemonCommandExecution.java:120)
    at org.gradle.launcher.daemon.server.exec.StartBuildOrRespondWithBusy$1.run(StartBuildOrRespondWithBusy.java:50)
    at org.gradle.launcher.daemon.server.DaemonStateCoordinator$1.run(DaemonStateCoordinator.java:297)
    at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:54)
    at org.gradle.internal.concurrent.StoppableExecutorImpl$1.run(StoppableExecutorImpl.java:40)
Caused by: java.lang.RuntimeException: java.lang.IllegalStateException: Unsupported type java.lang.String[]
    at com.sun.tools.javac.main.Main.compile(Main.java:553)
    at com.sun.tools.javac.api.JavacTaskImpl.doCall(JavacTaskImpl.java:129)
    at com.sun.tools.javac.api.JavacTaskImpl.call(JavacTaskImpl.java:138)
    at org.gradle.api.internal.tasks.compile.JdkJavaCompiler.execute(JdkJavaCompiler.java:46)
    at org.gradle.api.internal.tasks.compile.JdkJavaCompiler.execute(JdkJavaCompiler.java:33)
    at org.gradle.api.internal.tasks.compile.NormalizingJavaCompiler.delegateAndHandleErrors(NormalizingJavaCompiler.java:104)
    at org.gradle.api.internal.tasks.compile.NormalizingJavaCompiler.execute(NormalizingJavaCompiler.java:53)
    at org.gradle.api.internal.tasks.compile.NormalizingJavaCompiler.execute(NormalizingJavaCompiler.java:38)
    at org.gradle.api.internal.tasks.compile.CleaningJavaCompilerSupport.execute(CleaningJavaCompilerSupport.java:35)
    at org.gradle.api.internal.tasks.compile.CleaningJavaCompilerSupport.execute(CleaningJavaCompilerSupport.java:25)
    at org.gradle.api.tasks.compile.JavaCompile.performCompilation(JavaCompile.java:206)
    at org.gradle.api.tasks.compile.JavaCompile.compile(JavaCompile.java:187)
    at org.gradle.api.tasks.compile.JavaCompile.compile(JavaCompile.java:130)
    at com.android.build.gradle.tasks.factory.AndroidJavaCompile.compile(AndroidJavaCompile.java:49)
    at org.gradle.internal.reflect.JavaMethod.invoke(JavaMethod.java:73)
    at org.gradle.api.internal.project.taskfactory.DefaultTaskClassInfoStore$IncrementalTaskAction.doExecute(DefaultTaskClassInfoStore.java:163)
    at org.gradle.api.internal.project.taskfactory.DefaultTaskClassInfoStore$StandardTaskAction.execute(DefaultTaskClassInfoStore.java:134)
    at org.gradle.api.internal.project.taskfactory.DefaultTaskClassInfoStore$StandardTaskAction.execute(DefaultTaskClassInfoStore.java:123)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeAction(ExecuteActionsTaskExecuter.java:95)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:76)
    ... 78 more
Caused by: java.lang.IllegalStateException: Unsupported type java.lang.String[]
    at io.realm.processor.RealmProxyClassGenerator.getRealmTypeChecked(RealmProxyClassGenerator.java:2088)
    at io.realm.processor.RealmProxyClassGenerator.emitColumnInfoClass(RealmProxyClassGenerator.java:166)
    at io.realm.processor.RealmProxyClassGenerator.generate(RealmProxyClassGenerator.java:113)
    at io.realm.processor.RealmProcessor.processAnnotations(RealmProcessor.java:204)
    at io.realm.processor.RealmProcessor.process(RealmProcessor.java:157)
    at com.sun.tools.javac.processing.JavacProcessingEnvironment.callProcessor(JavacProcessingEnvironment.java:794)
    at com.sun.tools.javac.processing.JavacProcessingEnvironment.discoverAndRunProcs(JavacProcessingEnvironment.java:705)
    at com.sun.tools.javac.processing.JavacProcessingEnvironment.access$1800(JavacProcessingEnvironment.java:91)
    at com.sun.tools.javac.processing.JavacProcessingEnvironment$Round.run(JavacProcessingEnvironment.java:1035)
    at com.sun.tools.javac.processing.JavacProcessingEnvironment.doProcessing(JavacProcessingEnvironment.java:1176)
    at com.sun.tools.javac.main.JavaCompiler.processAnnotations(JavaCompiler.java:1170)
    at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:856)
    at com.sun.tools.javac.main.Main.compile(Main.java:523)
    ... 97 more

Doesn't appear to be a plugin or a library issue, I dropped everything back to the version before individually and the issue still occurred.

Answer 1

So just in case anyone runs into this same issue, it's because of Realm, if you extend RealmObject you can't have a String array or a list of Strings, so you have to use a little wrapper like the following:

public class RealmString extends RealmObject {
    public String string;
}

Then the following works:

public RealmList<RealmString> strings;

Hope this helps someone else in the future.