code: public static boolean unregister(String groupName) {
          groupName = normalizeGroupName(groupName);
          return serverGroups.remove(groupName) != null;
      }
docs: Unregisters the {@link EndpointGroup} with the specified case-insensitive {@code groupName}.
  Note that this is potentially a dangerous operation; make sure the {@code groupName} of the unregistered
  {@link EndpointGroup} is not in use by any clients.
  
  @return {@code true} if the {@link EndpointGroup} with the specified {@code groupName} has been removed.
  {@code false} if there's no such {@link EndpointGroup} in the registry.