Hi Team,

We are getting this error for the following API

https://172.30.X.X/ovirt-engine/api/disks?follow=statistics

But the following API works :

https://172.30.X.X/ovirt-engine/api/vms?follow=statistics

Error in server.log: (when we try to hit to the https://172.30.X.X/ovirt-engine/api/disks?follow=statistics)

2018-06-28 13:05:00,393+05 ERROR [io.undertow.request] (default task-2) UT005023: Exception handling request to /ovirt-engine/api/v4/disks: java.lang.RuntimeException: org.jboss.resteasy.spi.UnhandledException: java.lang.IllegalStateException: Problem following 'statistics' link in Disks entity.
        at io.undertow.servlet.spec.RequestDispatcherImpl.forwardImpl(RequestDispatcherImpl.java:245) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.spec.RequestDispatcherImpl.forwardImplSetup(RequestDispatcherImpl.java:147) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.spec.RequestDispatcherImpl.forward(RequestDispatcherImpl.java:111) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at org.ovirt.engine.api.restapi.invocation.VersionFilter.doFilter(VersionFilter.java:180) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.invocation.VersionFilter.doFilter(VersionFilter.java:98) [restapi-jaxrs.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at org.ovirt.engine.api.restapi.invocation.CurrentFilter.doFilter(CurrentFilter.java:117) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.invocation.CurrentFilter.doFilter(CurrentFilter.java:72) [restapi-jaxrs.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at org.ovirt.engine.core.aaa.filters.RestApiSessionMgmtFilter.doFilter(RestApiSessionMgmtFilter.java:78) [aaa.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at org.ovirt.engine.core.aaa.filters.EnforceAuthFilter.doFilter(EnforceAuthFilter.java:42) [aaa.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at org.ovirt.engine.core.aaa.filters.SsoRestApiNegotiationFilter.doFilter(SsoRestApiNegotiationFilter.java:84) [aaa.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at org.ovirt.engine.core.aaa.filters.SsoRestApiAuthFilter.doFilter(SsoRestApiAuthFilter.java:47) [aaa.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at org.ovirt.engine.core.aaa.filters.SessionValidationFilter.doFilter(SessionValidationFilter.java:59) [aaa.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at org.ovirt.engine.core.aaa.filters.RestApiSessionValidationFilter.doFilter(RestApiSessionValidationFilter.java:35) [aaa.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at org.ovirt.engine.api.restapi.security.CSRFProtectionFilter.doFilter(CSRFProtectionFilter.java:111) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.security.CSRFProtectionFilter.doFilter(CSRFProtectionFilter.java:102) [restapi-jaxrs.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at org.ovirt.engine.core.utils.servlet.CORSSupportFilter.doFilter(CORSSupportFilter.java:284) [utils.jar:]
        at io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:84) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) [undertow-core-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) [undertow-core-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.security.handlers.AuthenticationConstraintHandler.handleRequest(AuthenticationConstraintHandler.java:53) [undertow-core-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46) [undertow-core-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.security.ServletSecurityConstraintHandler.handleRequest(ServletSecurityConstraintHandler.java:59) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60) [undertow-core-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50) [undertow-core-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43) [undertow-core-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) [undertow-core-1.4.18.Final.jar:1.4.18.Final]
        at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) [undertow-core-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) [undertow-core-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:292) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.ServletInitialHandler.access$100(ServletInitialHandler.java:81) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:138) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:135) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.core.ServletRequestContextThreadSetupAction$1.call(ServletRequestContextThreadSetupAction.java:48) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.core.ContextClassLoaderSetupAction$1.call(ContextClassLoaderSetupAction.java:43) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at org.wildfly.extension.undertow.security.SecurityContextThreadSetupAction.lambda$create$0(SecurityContextThreadSetupAction.java:105)
        at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1508)
        at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1508)
        at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1508)
        at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:272) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:81) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:104) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.server.Connectors.executeRootHandler(Connectors.java:326) [undertow-core-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:812) [undertow-core-1.4.18.Final.jar:1.4.18.Final]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [rt.jar:1.8.0_161]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [rt.jar:1.8.0_161]
        at java.lang.Thread.run(Thread.java:748) [rt.jar:1.8.0_161]

Caused by: org.jboss.resteasy.spi.UnhandledException: java.lang.IllegalStateException: Problem following 'statistics' link in Disks entity.
        at org.jboss.resteasy.core.ExceptionHandler.handleApplicationException(ExceptionHandler.java:78) [resteasy-jaxrs-3.0.24.Final.jar:3.0.24.Final]
        at org.jboss.resteasy.core.ExceptionHandler.handleException(ExceptionHandler.java:222) [resteasy-jaxrs-3.0.24.Final.jar:3.0.24.Final]
        at org.jboss.resteasy.core.SynchronousDispatcher.writeException(SynchronousDispatcher.java:179) [resteasy-jaxrs-3.0.24.Final.jar:3.0.24.Final]
        at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:422) [resteasy-jaxrs-3.0.24.Final.jar:3.0.24.Final]
        at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:213) [resteasy-jaxrs-3.0.24.Final.jar:3.0.24.Final]
        at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:228) [resteasy-jaxrs-3.0.24.Final.jar:3.0.24.Final]
        at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:56) [resteasy-jaxrs-3.0.24.Final.jar:3.0.24.Final]
        at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:51) [resteasy-jaxrs-3.0.24.Final.jar:3.0.24.Final]
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) [jboss-servlet-api_3.1_spec-1.0.0.Final.jar:1.0.0.Final]
        at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:81) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) [undertow-core-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) [undertow-core-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) [undertow-core-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:274) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.handlers.ServletInitialHandler.dispatchToPath(ServletInitialHandler.java:209) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        at io.undertow.servlet.spec.RequestDispatcherImpl.forwardImpl(RequestDispatcherImpl.java:221) [undertow-servlet-1.4.18.Final.jar:1.4.18.Final]
        ... 73 more
Caused by: java.lang.IllegalStateException: Problem following 'statistics' link in Disks entity.
        at org.ovirt.engine.api.restapi.resource.utils.LinkFollower.fetchData(LinkFollower.java:185) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.resource.utils.LinkFollower.followLink(LinkFollower.java:144) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.resource.utils.LinkFollower.followLinks(LinkFollower.java:132) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.resource.utils.LinkFollower.followLinks(LinkFollower.java:53) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.resource.BaseBackendResource.follow(BaseBackendResource.java:412) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.resource.DisksResource.doList(DisksResource.java:222) [restapi-definition.jar:]
        at sun.reflect.GeneratedMethodAccessor684.invoke(Unknown Source) [:1.8.0_161]
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) [rt.jar:1.8.0_161]
        at java.lang.reflect.Method.invoke(Method.java:498) [rt.jar:1.8.0_161]
        at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:140) [resteasy-jaxrs-3.0.24.Final.jar:3.0.24.Final]
        at org.jboss.resteasy.core.ResourceMethodInvoker.invokeOnTarget(ResourceMethodInvoker.java:295) [resteasy-jaxrs-3.0.24.Final.jar:3.0.24.Final]
        at org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:249) [resteasy-jaxrs-3.0.24.Final.jar:3.0.24.Final]
        at org.jboss.resteasy.core.ResourceLocatorInvoker.invokeOnTargetObject(ResourceLocatorInvoker.java:138) [resteasy-jaxrs-3.0.24.Final.jar:3.0.24.Final]
        at org.jboss.resteasy.core.ResourceLocatorInvoker.invoke(ResourceLocatorInvoker.java:101) [resteasy-jaxrs-3.0.24.Final.jar:3.0.24.Final]
        at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:406) [resteasy-jaxrs-3.0.24.Final.jar:3.0.24.Final]
        ... 88 more
Caused by: java.lang.IllegalStateException: Problem fetching 'statistics' from Disk
        at org.ovirt.engine.api.restapi.resource.utils.LinkFollower.fetchData(LinkFollower.java:219) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.resource.utils.LinkFollower.fetchData(LinkFollower.java:182) [restapi-jaxrs.jar:]
        ... 102 more
Caused by: java.lang.NullPointerException
        at org.ovirt.engine.api.restapi.resource.utils.LinkFollower.getHref(LinkFollower.java:250) [restapi-jaxrs.jar:]
        at org.ovirt.engine.api.restapi.resource.utils.LinkFollower.fetchData(LinkFollower.java:211) [restapi-jaxrs.jar:]
        ... 103 more

Thanks,

Hari