[SalesForce] Check if Record Exists before Insert To Avoid Duplicates

Calling all Apex Professionals !

I am attempting to write a requirement in my class that will check if there is already a record in our system before I insert the records so that I will not have duplicate records, however when I run the code as it is now I am not getting any records to load what so ever.. Could anyone take a stab at this for me ??

for (Object vacationRequestWrapper : vacationRequests) {
                Map<String, Object> vacationRequest = (Map<String, Object>) vacationRequestWrapper;
                if (vacationRequest.get('status').equals('approved')) {
                    system.debug('vacationRequests ' + vacationRequest);
                    Map<String, Object> wrapper3 = (Map<String, Object>) vacationRequest.get('creator');

                    Map<String,Object> empValues = new Map<String,Object>(); 

                    string ptoUrl = (String) wrapper3.get('url');

                    empValues.put('startDate',vacationRequest.get('start_date'));
                    empValues.put('endDate',vacationRequest.get('end_date'));
                    empValues.put('ptoId',vacationRequest.get('id'));
                    string ptoId = (string)vacationRequest.get('id');
                    string employeeId = ptoUrl.substring(ptoUrl.length() - 7, ptoUrl.length() - 0);
                    empMap.put(employeeId, empvalues);
                    ptoMap.put(ptoId, empvalues);
                    system.debug('ptoMap ' + ptoMap);
                    system.debug('empMap'+ empMap);
                }
            }
                    Map<String, Object> tempEmpValues = new Map<String, Object>();
                    Map<String,Object> contactVal = new Map<String,Object>();

                    List<Contact> contactList = [SELECT Id, FirstName, LastName, Zenefits_ID__c FROM Contact WHERE Zenefits_ID__c IN : empMap.keySet() LIMIT 200];
                    for (Contact con : contactList) {
                        System.debug('contactList ' + contactList); 

                        tempEmpValues = empMap.get(con.Zenefits_ID__C);
                        contactVal.put('ConId', con.id);
                    }

                        List<Time_Off_Request__c> torList = [SELECT ID, Zenefits_ID__c FROM Time_Off_Request__c WHERE Zenefits_ID__c NOT IN : ptoMap.keySet() LIMIT 200];
                        system.debug('torlist ' + torList);
                        for(Time_Off_Request__c tor1 : torList) {
                            if(tor1.Zenefits_Id__c == (String)ptoMap.get('ptoId')){
                                return Null;
                                 } else {
                                         Time_Off_Request__c tor = new Time_Off_Request__c();
                                         tor.Employee__c =(string)contactVal.get('ConId');
                                         tor.Project__c = 'a8q8A000000CafTQAS';
                                         tor.First_Day_Off__c = date.valueof((string)tempEmpValues.get('startDate'));
                                         tor.Last_Day_Off__c = date.valueof((string)tempEmpValues.get('endDate'));
                                         tor.Status__c = 'Approved';
                                         tor.Zenefits_ID__c = (string)tempEmpValues.get('ptoId');
                                         torToUpdate.add(TOR);
                                         system.debug('torToUpdate' + torToUpdate); 


                                }
                            }                    
                        }
                    }

                }
            return nextUrl;
            }
        }

I have shortened the class to really only show what we aree concerned about, but the list that I am using a SOQL query against that is throwing things off or giving me grief is..

 List<Time_Off_Request__c> torList = [SELECT ID, Zenefits_ID__c FROM Time_Off_Request__c WHERE Zenefits_ID__c NOT IN : ptoMap.keySet() LIMIT 200];

Is the reason why the insert is inserting zero records due to the fact that the torList returns NULL?

At this time I have literally 0 Time_Off_Request__c records in my developer SB so it should return null, but then it should go ahead and create the Time_Off_Request__c records for all oother records.

Basically I need the code to search my system's Time_Off_Request__c records and check if the Zenefits_Id__c is equal to the ptoId (which is the Key in the ptoMap) and if they do match then I do not want those records to be inserted, but for all records that do not have a match I want the records to be inserted