NPE in sample/java-spring-boot-mvc

[aanno2]

This is a bug report (I'm only use the pull request feature to make it easy for everyone to see what I changed).

I modified the sources under sample/java-spring-boot-mvc. With gradle 3.5.1 the following happens:

$ gradle generateSwaggerDocumentation --stacktrace
:compileJava UP-TO-DATE
:processResources UP-TO-DATE
:classes UP-TO-DATE
:generateSwaggerDocumentation FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':generateSwaggerDocumentation'.
> org.gradle.api.GradleException (no error message)

* Try:
Run with --info or --debug option to get more log output.

* Exception is:
org.gradle.api.tasks.TaskExecutionException: Execution failed for task ':generateSwaggerDocumentation'.
        at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:98)
        at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:68)
        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)