RH-SSO won't start with error: "hostname not set"

Issue

• Server won't startup: MSC000001: Failed to start service jboss.deployment.unit."keycloak-server.war" with stack trace:

      at org.wildfly.extension.undertow.deployment.UndertowDeploymentService$1.run(UndertowDeploymentService.java:81)
      at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
      ...
  Caused by: java.lang.RuntimeException: RESTEASY003325: Failed to construct public org.keycloak.services.resources.KeycloakApplication(javax.servlet.ServletContext,org.jboss.resteasy.core.Dispatcher)
      at org.jboss.resteasy.core.ConstructorInjectorImpl.construct(ConstructorInjectorImpl.java:166)
      at org.jboss.resteasy.spi.ResteasyProviderFactory.createProviderInstance(ResteasyProviderFactory.java:2757)
      ...
      at io.undertow.servlet.core.ContextClassLoaderSetupAction$1.call(ContextClassLoaderSetupAction.java:43)
      at org.wildfly.extension.undertow.security.SecurityContextThreadSetupAction.lambda$create$0(SecurityContextThreadSetupAction.java:105)
      ...
      at org.wildfly.extension.undertow.deployment.UndertowDeploymentService$1.run(UndertowDeploymentService.java:78)
      ... 8 more
  Caused by: java.lang.RuntimeException: hostname not set
      at org.keycloak.url.FixedHostnameProviderFactory.init(FixedHostnameProviderFactory.java:24)
      at org.keycloak.services.DefaultKeycloakSessionFactory.loadFactories(DefaultKeycloakSessionFactory.java:217)
      at org.keycloak.services.DefaultKeycloakSessionFactory.init(DefaultKeycloakSessionFactory.java:78)
      at org.keycloak.services.resources.KeycloakApplication.createSessionFactory(KeycloakApplication.java:331)
      at org.keycloak.services.resources.KeycloakApplication.<init>(KeycloakApplication.java:118)
      at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
      at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
      at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
      at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
      at org.jboss.resteasy.core.ConstructorInjectorImpl.construct(ConstructorInjectorImpl.java:154)
      ... 31 more