Cannot read field "mutatorFacetType" because "mutatorSpec" is null

Reproduce via:
kroviz (running against nightly Docker Image) -> Demo -> Basic Types -> Strings

Url:
http://localhost:8080/restful/objects/demo.JavaLangStrings/PADw_eG1sIHZlcnNpb249IjEuMCIgZW5jb2Rpbmc9IlVURi04IiBzdGFuZGFsb25lPSJ5ZXMiPz4KPERlbW8vPgo=/collections/entities

Stacktrace:
org.apache.isis.viewer.restfulobjects.rendering.domainobjects.AbstractObjectMemberReprRenderer.addLinkFor(AbstractObjectMemberReprRenderer.java:226)
org.apache.isis.viewer.restfulobjects.rendering.domainobjects.ObjectCollectionReprRenderer.addMutatorLink(ObjectCollectionReprRenderer.java:169)
org.apache.isis.viewer.restfulobjects.rendering.domainobjects.ObjectCollectionReprRenderer.addMutatorLinksIfEnabled(ObjectCollectionReprRenderer.java:160)
org.apache.isis.viewer.restfulobjects.rendering.domainobjects.AbstractObjectMemberReprRenderer.renderMemberContent(AbstractObjectMemberReprRenderer.java:194)
org.apache.isis.viewer.restfulobjects.rendering.domainobjects.ObjectCollectionReprRenderer.render(ObjectCollectionReprRenderer.java:67)
org.apache.isis.viewer.restfulobjects.rendering.Responses.ofOk(Responses.java:67)
org.apache.isis.viewer.restfulobjects.rendering.service.conneg.ContentNegotiationServiceForRestfulObjectsV1_0.buildResponseTo(ContentNegotiationServiceForRestfulObjectsV1_0.java:183)
org.apache.isis.viewer.restfulobjects.rendering.service.conneg.ContentNegotiationServiceForRestfulObjectsV1_0.buildResponse(ContentNegotiationServiceForRestfulObjectsV1_0.java:161)
org.apache.isis.viewer.restfulobjects.rendering.service.RepresentationService.lambda$collectionDetails$2(RepresentationService.java:151)
org.apache.isis.viewer.restfulobjects.rendering.service.RepresentationService.buildResponse(RepresentationService.java:222)
org.apache.isis.viewer.restfulobjects.rendering.service.RepresentationService.collectionDetails(RepresentationService.java:150)
org.apache.isis.viewer.restfulobjects.viewer.resources.DomainResourceHelper.collectionDetails(DomainResourceHelper.java:133)
org.apache.isis.viewer.restfulobjects.viewer.resources.DomainObjectResourceServerside.accessCollection(DomainObjectResourceServerside.java:526)
java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:64)
java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.base/java.lang.reflect.Method.invoke(Method.java:564)
org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:170)
org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:130)
org.jboss.resteasy.core.ResourceMethodInvoker.internalInvokeOnTarget(ResourceMethodInvoker.java:646)
org.jboss.resteasy.core.ResourceMethodInvoker.invokeOnTargetAfterFilter(ResourceMethodInvoker.java:510)
org.jboss.resteasy.core.ResourceMethodInvoker.lambda$invokeOnTarget$2(ResourceMethodInvoker.java:460)
org.jboss.resteasy.core.interception.jaxrs.PreMatchContainerRequestContext.filter(PreMatchContainerRequestContext.java:364)
org.jboss.resteasy.core.ResourceMethodInvoker.invokeOnTarget(ResourceMethodInvoker.java:462)
org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:420)
org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:394)
org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:69)
org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:492)
org.jboss.resteasy.core.SynchronousDispatcher.lambda$invoke$4(SynchronousDispatcher.java:261)
org.jboss.resteasy.core.SynchronousDispatcher.lambda$preprocess$0(SynchronousDispatcher.java:161)
org.jboss.resteasy.core.interception.jaxrs.PreMatchContainerRequestContext.filter(PreMatchContainerRequestContext.java:364)
org.jboss.resteasy.core.SynchronousDispatcher.preprocess(SynchronousDispatcher.java:164)
org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:247)
org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:249)
org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:60)
org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:55)
javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
org.apache.isis.viewer.restfulobjects.viewer.webmodule.IsisRestfulObjectsInteractionFilter.lambda$doFilter$1(IsisRestfulObjectsInteractionFilter.java:387)
org.apache.isis.commons.functional.ThrowingRunnable.lambda$toCallable$0(ThrowingRunnable.java:36)
org.apache.isis.commons.functional.Result.of(Result.java:58)
org.apache.isis.core.runtimeservices.transaction.TransactionServiceSpring.callTransactional(TransactionServiceSpring.java:106)
org.apache.isis.applib.services.xactn.TransactionalProcessor.callWithinCurrentTransactionElseCreateNew(TransactionalProcessor.java:100)
org.apache.isis.applib.services.xactn.TransactionalProcessor.runWithinCurrentTransactionElseCreateNew(TransactionalProcessor.java:110)
org.apache.isis.viewer.restfulobjects.viewer.webmodule.IsisRestfulObjectsInteractionFilter.lambda$doFilter$3(IsisRestfulObjectsInteractionFilter.java:386)
org.apache.isis.core.runtimeservices.session.InteractionFactoryDefault.runAuthenticated(InteractionFactoryDefault.java:268)
org.apache.isis.viewer.restfulobjects.viewer.webmodule.IsisRestfulObjectsInteractionFilter.doFilter(IsisRestfulObjectsInteractionFilter.java:382)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
org.apache.isis.core.webapp.modules.logonlog.IsisLogOnExceptionFilter.doFilter(IsisLogOnExceptionFilter.java:60)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
org.apache.shiro.web.servlet.AbstractShiroFilter.executeChain(AbstractShiroFilter.java:450)
org.apache.shiro.web.servlet.AbstractShiroFilter$1.call(AbstractShiroFilter.java:365)
org.apache.shiro.subject.support.SubjectCallable.doCall(SubjectCallable.java:90)
org.apache.shiro.subject.support.SubjectCallable.call(SubjectCallable.java:83)
org.apache.shiro.subject.support.DelegatingSubject.execute(DelegatingSubject.java:387)
org.apache.shiro.web.servlet.AbstractShiroFilter.doFilterInternal(AbstractShiroFilter.java:362)
org.apache.shiro.web.servlet.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:125)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
org.springframework.web.filter.CorsFilter.doFilterInternal(CorsFilter.java:91)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.doFilterInternal(WebMvcMetricsFilter.java:93)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542)
org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:357)
org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374)
org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:893)
org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1707)
org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
java.base/java.lang.Thread.run(Thread.java:832)