Cannot access RH-SSO admin console

Issue

• After login to the RH-SSO admin console we see blank screen

• The following error is logged in server.log file:

  ERROR [org.keycloak.services.error.KeycloakErrorHandler] (default task-8) Uncaught server error: java.lang.NullPointerException
      at org.keycloak.services.resources.admin.AdminConsole.addMasterRealmAccess(AdminConsole.java:242)
      at org.keycloak.services.resources.admin.AdminConsole.whoAmI(AdminConsole.java:215)
      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)
  ...