I have seen many posts with the same title but none of the provided answers explains why does this error occur.

EDIT: My goal is to add another value to an existing case. I want to populate this case field: User_Agent__c with the a value from the LiveChatTranscript record. The existing case has already data stored in it and of course I don't want to override it.

 Trigger Chat_copyUserAgentToNewCase on LiveChatTranscript(before insert) {
     List < Case > lstcases = new List < Case > ();
     for (LiveChatTranscript trans: Trigger.new) {
         if (trans.UserAgent != null) {
             Case c = new Case(Id = trans.CaseId, User_Agent__c = trans.UserAgent);
     if (!lstcases.isEmpty()) {
         update lstcases; // on this row I get the error

  • in case if you create new case, you need to insert that, not update – kurunve Jun 26 '17 at 7:05
  • Do you need to insert a new case or update en existing case? This is really not clear. – Martin Lezer Jun 26 '17 at 7:09
  • I am updating an existing case, I want to populate the field User_Agent__c on the existing case with trans.UserAgent – Json Jun 26 '17 at 7:27

This code changes will stop the error (by ignoring records that don't have a Case Id):

     Map<Id, Case> cases = new Map<Id, Case>();
     if (trans.CaseId != null && trans.UserAgent != null) {
         Case c = new Case(Id = trans.CaseId, User_Agent__c = trans.UserAgent);
         cases.put(c.Id, c);
     update cases.values();

Using a Map ensures there will never be two records of the same Id in the update (which would throw an error).

| improve this answer | |
  • Thanks @Keith C, quick question: is it not recommended to check if the list/map is not empty before executing DML operation? – Json Jun 26 '17 at 9:41
  • @Dante Originally DML on empty lists did count against limits but that was addressed many API versions ago so no need to check. – Keith C Jun 26 '17 at 9:44

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