Gradle Guides, Building Java Web Application - Gradle build throwing java.lang.IllegalStateException

The "Building Java Web Application" guide does not work with Gradle v6.2.2. When I try to build the webdemo, gradle throws an IllegalStateException, "The configuration :grettyNoSpringBoot was resolved from a thread not managed by Gradle."

```
% ./gradlew build (git)-[master]
Exception in thread "Thread-447" java.lang.IllegalStateException: The configuration :grettyNoSpringBoot was resolved from a thread not managed by Gradle.
at org.gradle.api.internal.artifacts.configurations.DefaultConfiguration.resolveToStateOrLater(DefaultConfiguration.java:565)
at org.gradle.api.internal.artifacts.configurations.DefaultConfiguration.access$1900(DefaultConfiguration.java:141)
at org.gradle.api.internal.artifacts.configurations.DefaultConfiguration$ConfigurationFileCollection.getSelectedArtifacts(DefaultConfiguration.java:1246)
at org.gradle.api.internal.artifacts.configurations.DefaultConfiguration$ConfigurationFileCollection.visitContents(DefaultConfiguration.java:1237)
at org.gradle.api.internal.artifacts.configurations.DefaultConfiguration$ConfigurationFileCollection.getFiles(DefaultConfiguration.java:1226)
at org.gradle.api.internal.artifacts.configurations.DefaultConfiguration.getFiles(DefaultConfiguration.java:484)
at org.gradle.api.internal.artifacts.configurations.DefaultConfiguration_Decorated.getFiles(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:101)
at groovy.lang.MetaBeanProperty.getProperty(MetaBeanProperty.java:59)
at org.gradle.internal.metaobject.BeanDynamicObject$MetaClassAdapter.getProperty(BeanDynamicObject.java:232)
at org.gradle.internal.metaobject.BeanDynamicObject.tryGetProperty(BeanDynamicObject.java:175)
at org.gradle.internal.metaobject.CompositeDynamicObject.tryGetProperty(CompositeDynamicObject.java:55)
at org.gradle.internal.metaobject.AbstractDynamicObject.getProperty(AbstractDynamicObject.java:59)
at org.gradle.api.internal.artifacts.configurations.DefaultConfiguration_Decorated.getProperty(Unknown Source)
at org.codehaus.groovy.runtime.callsite.PogoGetPropertySite.getProperty(PogoGetPropertySite.java:49)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callGetProperty(AbstractCallSite.java:298)
at org.akhikhl.gretty.DefaultLauncher.getRunnerClassPath(DefaultLauncher.groovy:33)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:101)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:323)
at org.gradle.internal.metaobject.BeanDynamicObject$MetaClassAdapter.invokeMethod(BeanDynamicObject.java:483)
at org.gradle.internal.metaobject.BeanDynamicObject.tryInvokeMethod(BeanDynamicObject.java:195)
at org.gradle.internal.metaobject.ConfigureDelegate.invokeMethod(ConfigureDelegate.java:77)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeOnDelegationObjects(ClosureMetaClass.java:397)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:337)
at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.callCurrent(PogoMetaClassSite.java:64)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:176)
at org.akhikhl.gretty.DefaultLauncher$_javaExec_closure7.doCall(DefaultLauncher.groovy:94)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:101)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:323)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:263)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1041)
at groovy.lang.Closure.call(Closure.java:405)
at groovy.lang.Closure.call(Closure.java:421)
at org.gradle.util.ClosureBackedAction.execute(ClosureBackedAction.java:71)
at org.gradle.util.ConfigureUtil.configureTarget(ConfigureUtil.java:154)
at org.gradle.util.ConfigureUtil.configure(ConfigureUtil.java:105)
at org.gradle.util.ConfigureUtil$WrappedConfigureAction.execute(ConfigureUtil.java:166)
at org.gradle.process.internal.DefaultExecActionFactory.javaexec(DefaultExecActionFactory.java:144)
at org.gradle.api.internal.project.DefaultProject.javaexec(DefaultProject.java:1129)
at org.gradle.api.internal.project.DefaultProject.javaexec(DefaultProject.java:1124)
at org.gradle.api.Project$javaexec$6.call(Unknown Source)
at org.akhikhl.gretty.DefaultLauncher.javaExec(DefaultLauncher.groovy:93)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:101)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:323)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:351)
at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.callCurrent(PogoMetaClassSite.java:64)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callCurrent(AbstractCallSite.java:168)
at org.akhikhl.gretty.LauncherBase$_launchThread_closure4.doCall(LauncherBase.groovy:259)
at org.akhikhl.gretty.LauncherBase$_launchThread_closure4.doCall(LauncherBase.groovy)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:101)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:323)
at org.codehaus.groovy.runtime.metaclass.ClosureMetaClass.invokeMethod(ClosureMetaClass.java:263)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1041)
at groovy.lang.Closure.call(Closure.java:405)
at groovy.lang.Closure.call(Closure.java:399)
at groovy.lang.Closure.run(Closure.java:486)
at java.lang.Thread.run(Thread.java:748)
```

Start with the Building Java Web Application guide and reproduce the failure by running ./gradlew build with Gradle v6.2.2 for the webdemo. Trace the grettyNoSpringBoot configuration and confirm the guide builds without the reported IllegalStateException.

Written by the indexing model from the issue text.