Hi All, 
        i have a batch class in which i am migrating the users(Contact in salesforce) from Zendesk. so i created a batch and make an Api call to Zendesk to fetch All the contacts of Zendesk.
but when i run the batch the Apex job is showing Argument can not be null. what is the issue?
is it related to Contact's Account. i have some contact in Zendesk that dont have any parent Account.i am trying to debug but the debug log is blank.
Any suggestions how to solve the issue?
My Batch class is given below:-
public class BatchZendeskToSalesforceCon implements Database.Batchable<sObject>,Database.AllowsCallouts, Database.Stateful{
    public Database.querylocator start(Database.BatchableContext BC){
        string query;
        query = 'SELECT Id, Name,Email, Zd_url__c, External_Id__c, Custom_Role_id__c, Zd_ticket_restriction__c,'+
            'Zd_Organisation_id__c, Zd_report_csv__c, Zd_Suspended__c, locale__c, Zd_Tags__c,'+
            'Zd_two_factor_auth_enabled__c, Zd_verified__c, Active__c, Role_Type__c, Alias__c,'+
            'Moderator__c, Only_private_Comments__c, Zendesk_Id__c, Zd_default_group_id__c,'+
            'Zd_Restricted_Agent__c, phone, Zd_Shared__c, Notes__c, locale_id__c, Zd_time_zone__c,'+
            'Zd_Shared_phone_number__c, Zd_Shared_agent__c, Chat_only__c, Zd_Signature__c ' +
            'FROM Contact ';
        //System.assert( FALSE, query );
        return Database.getQueryLocator(query);
    }
    public void execute( Database.BatchableContext BC, List<Contact> Contacts){
        
        Set<Id> contactIds = new Set<Id>();
        for( Contact con : Contacts ){
            contactIds.add( con.Id );   
        }
        //System.assert(false, contactIds);
        getContacts();
    }
    
    public static void getContacts(){
        //ZendeskApis.ZendeskContactApi();
        HttpRequest req = new HttpRequest();
        req.setMethod( 'GET' );
        String username = 'kevin@sfdcconsultants.com';
        String password = '45j2JpHB^qy*';
        Blob headerValue = Blob.valueOf( username + ':' + password );
        String authorizationHeader = 'BASIC ' + EncodingUtil.base64Encode( headerValue );
        req.setHeader( 'Authorization', authorizationHeader );
        req.setHeader( 'Content-Type', 'application/json' );
        req.setEndpoint( 'https://timerack.zendesk.com/api/v2/users.json' );
        Http binding = new Http();
        HttpResponse res = binding.send( req );
        
        Map<String, Object> results = ( Map<String, Object> )JSON.deserializeUntyped( res.getBody() );
        
       // system.assert(false,results);
        
        List<Object> lstUsers = ( List<Object> )results.get( 'users' );
        List<Map<String, Object>> customerAtt = new List< Map< String, Object >>();
        for ( Object customer : lstUsers ) {
            Map<String, Object> customerAttributes = ( Map< String, Object >)customer;
            customerAtt.add( customerAttributes );
        }
        List< Contact > listContactToUpsert = new List< Contact >();
        for( Map< String, Object> attMap : customerAtt ){
            Contact ct = new Contact();
            String fullName = String.valueOf( attMap.get( 'name' ));
            if( fullName.split(' ').size() > 1 ){
                ct.FirstName = fullName.substring( 0, fullName.indexOf(' ') );
                ct.LastName = fullName.substring( fullName.indexOf(' ') + 1 );
            }else{
                ct.LastName = fullName;
            }
            ct.Zendesk_Id__c = String.valueOf(attMap.get( 'id' ));
            System.debug('Zendesk id'+ct.Zendesk_Id__c);
            ct.email = String.valueOf( attMap.get( 'email' ));
                        System.debug('Zendesk id'+ct.email);

            ct.Zd_url__c =  String.valueOf( attMap.get( 'url' ));
                        System.debug('Zendesk id'+ct.Zd_url__c);

            ct.Zd_time_zone__c = String.valueOf(attMap.get('time_zone'));
                        System.debug('Zendesk id'+ct.Zd_time_zone__c);

            ct.Zd_iana_time_zone__c = String.valueOf( attMap.get( 'iana_time_zone' ));
                        System.debug('Zendesk id'+ct.Zd_iana_time_zone__c);

            ct.phone = String.valueOf( attMap.get( 'phone' ));
                        System.debug('Zendesk id'+ct.phone);

            ct.Zd_Shared_phone_number__c = Boolean.valueOf( attMap.get( 'shared_phone_number' ));
                        System.debug('Zendesk id'+ct.Zd_Shared_phone_number__c);

            ct.Photo__c = String.valueOf( attMap.get( 'photo' ));
                        System.debug('Zendesk id'+ct.Photo__c);

            ct.locale__c = String.valueOf( attMap.get( 'locale' ));
            System.debug('Zendesk id'+ct.locale__c);

            ct.locale_id__c =  Integer.valueOf(attMap.get('locale_id'));
            System.debug('Zendesk id'+ct.locale_id__c);

            ct.Zd_Organisation_id__c = String.valueOf( attMap.get( 'organization_id' ));
             System.debug('Zendesk id'+ct.Zd_Organisation_id__c);

            ct.Zd_role__c =  String.valueOf( attMap.get( 'role' ));
                System.debug('Zendesk id'+ ct.Zd_role__c);

            ct.Zd_verified__c = Boolean.valueOf( attMap.get( 'verified' ));
                 System.debug('Zendesk id'+ct.Zd_verified__c);

            ct.External_Id__c = String.valueOf( attMap.get( 'external_id' ));
                        System.debug('Zendesk id'+ct.External_Id__c);

            ct.Zd_Tags__c = String.valueOf(attMap.get('tags'));
                        System.debug('Zendesk id'+ct.Zd_Tags__c);

            ct.Alias__c = String.valueOf( attMap.get( 'alias' ));
                        System.debug('Zendesk id'+ct.Alias__c);

            ct.Active__c = Boolean.valueOf( attMap.get( 'active' ));
                        System.debug('Zendesk id'+ct.Active__c);

            ct.Zd_Shared__c = Boolean.valueOf( attMap.get( 'shared' ));
                        System.debug('Zendesk id'+ct.Zd_Shared__c);

            ct.Zd_Shared_agent__c = Boolean.valueOf( attMap.get( 'shared_agent' ));
                        System.debug('Zendesk id'+ct.Zd_Shared_agent__c);

            ct.Zd_last_login_at__c = Date.valueOf( attMap.get( 'last_login_at' ));
                        System.debug('Zendesk id'+ct.Zd_last_login_at__c);

            ct.Zd_two_factor_auth_enabled__c = Boolean.valueOf(attMap.get('two_factor_auth_enabled'));
                        System.debug('Zendesk id'+ct.Zd_two_factor_auth_enabled__c);

            ct.Zd_Signature__c = String.valueOf(attMap.get('signature'));
                        System.debug('Zendesk id'+ct.Zd_Signature__c);

            ct.Notes__c = String.valueOf( attMap.get( 'notes' ));
                        System.debug('Zendesk id'+ct.Notes__c);

            ct.Role_Type__c = Integer.valueOf( attMap.get( 'role_type' ));
                        System.debug('Zendesk id'+ct.Role_Type__c);

            ct.Custom_Role_id__c =  Integer.valueOf(attMap.get('custom_role_id'));
                        System.debug('Zendesk id'+ct.Custom_Role_id__c);

            ct.Moderator__c = Boolean.valueOf(attMap.get('moderator'));
                        System.debug('Zendesk id'+ct.Moderator__c);

            ct.Zd_ticket_restriction__c = String.valueOf(attMap.get('ticket_restriction'));
                        System.debug('Zendesk id'+ct.Zd_ticket_restriction__c);

            ct.Only_private_Comments__c = Boolean.valueOf( attMap.get( 'only_private_comments' ));
                        System.debug('Zendesk id'+ct.Only_private_Comments__c);

            ct.Zd_Restricted_Agent__c = Boolean.valueOf( attMap.get( 'restricted_agent' ));
                        System.debug('Zendesk id'+ct.Zd_Restricted_Agent__c);

            ct.Zd_Suspended__c = Boolean.valueOf( attMap.get( 'suspended' ));
                        System.debug('Zendesk id'+ct.Zd_Suspended__c);

            ct.Chat_only__c = Boolean.valueOf( attMap.get( 'chat_only' ));
                        System.debug('Zendesk id'+ct.Chat_only__c);

            ct.Zd_default_group_id__c = Integer.valueOf( attMap.get( 'default_group_id' ));
                        System.debug('Zendesk id'+ct.Zd_default_group_id__c);

            ct.Zd_report_csv__c = Boolean.valueOf( attMap.get( 'report_csv' ));
                        System.debug('Zendesk id'+ct.Zd_report_csv__c);

            
            listContactToUpsert.add(ct);
            /*if(ct.Name == 'testBC'){
               System.assert(false, listContactToUpsert);
              }*/
        }
        insert listContactToUpsert;
    }
    public void finish(Database.BatchableContext BC){
        
    }  
    
}