 public static void matchExisting(Set<Id> userIds) {     // Find the Chatter group Ids from the names of the custom setting "Chatter Auto Follow"     List<CollaborationGroup> chatterGroups = [SELECT Id                                                FROM CollaborationGroup                                                WHERE Name in :Chatter_Auto_Follow__c.getall().keySet()];      // Query for existing chatter group records     List<CollaborationGroupMember> cGMember = [SELECT   Id,                                                          MemberId,                                                         CollaborationGroupId                                                FROM     CollaborationGroupMember                                                 WHERE    MemberId IN :userIds AND                                                          CollaborationGroupId IN :chatterGroups];      System.debug('member size is:: ' + cGMember.size());      