@Override
  public void setGroups(String[] groups) {
    if (groups == null) {
      this.groups = CacheServer.DEFAULT_GROUPS;
    } else if (groups.length > 0) {
      // copy it for isolation
      String[] copy = new String[groups.length];
      System.arraycopy(groups, 0, copy, 0, groups.length);
      this.groups = copy;
    } else {
      this.groups = CacheServer.DEFAULT_GROUPS; // keep findbugs happy
    }
  }
Method to create & send the ClientMembershipMessage to admin members. The message is sent
only if there are any admin members in the distribution system.

@param event describes a change in client membership
@param type type of event - one of ClientMembershipMessage.JOINED,
       ClientMembershipMessage.LEFT, ClientMembershipMessage.CRASHED
geode-core/src/main/java/org/apache/geode/internal/cache/AbstractCacheServer.java