In Development Guide, link to SingletonServiceBuilder has an extra "/" in the URL:
/access.redhat.com/webassets/avalon/d/jboss_enterprise_application_platform_continuous_delivery/15/javadocs*//*org/wildfly/clustering/singleton/SingletonServiceBuilder.html

Please correct, and scan through our guides for additional instances of "//".

nziakova@redhat.com, thank you for catching the issue!