I have this method that below that Returns String of Id's separated by '|' operator. Now I would like to add on this  if and Id is null or blank replace with just single quotes (''). Not sure how to do that. How can i modify this method to do that.

    public static string getString(Set<Id> setId)
           {
               String strId = '';
               if(setId != null && setId.size() > 0 )
               {
                    for(Id RecordId :setId)
                    {
                        String strRecordId = RecordId;
                        if(strRecordId.length() > 15){
                            strRecordId = strRecordId.substring(0,15);
                        }
                        strRecordId = '\''+ strRecordId + '\'';
                        strId += strRecordId + '|';
                    }
                    strId = strId.removeEnd('|');
               } 
               return strId;
           }