Hi everyone, I hope someone can give me a sollution. It is not possible for our users to convert a lead without an opportunity. I will copy the errors below and the Apex Class LeadUtil. Also I will so the place where I think the Apex Code is not corrert. 

This is the error in the debug log:

11:18:09.125 (1125730322)|METHOD_EXIT|[2]|01pw0000003wWyK|LeadUtil.entry(LeadUtil.TriggerParams) 11:18:09.125 (1125865020)|FATAL_ERROR|System.NullPointerException: Attempt to de-reference a null object Class.LeadUtil.entry: line 104, column 1 Trigger.LeadTrigger: line 2, column 1 11:18:09.125 (1125880838)|FATAL_ERROR|System.NullPointerException: Attempt to de-reference a null object


This is error on the User interface:
Error: System.DmlException: Update failed. First exception on row 0 with id 00Qw000000nUFTUEA4; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, LeadTrigger: execution of BeforeUpdate caused by: System.NullPointerException: Attempt to de-reference a null object Class.LeadUtil.entry: line 104, column 1 Trigger.LeadTrigger: line 2, column 1: [] (System Code)

I think this is place in code which has to be changed:
        //l.ConvertedOpportunityId, l.ConvertedContactId
                  if(rt.DeveloperName == 'PersonAccount'){
                    Opportunity opp = (l.ConvertedOpportunityId != null) ? new Opportunity(id=l.ConvertedOpportunityId): null;
                    

This is the full Apex LeadUtil:
public class LeadUtil {
//ab
    //Contains all trigger information
    public class TriggerParams {

        public Boolean isBefore;
        public Boolean isAfter;
        public Boolean isInsert;
        public Boolean isUpdate;
        public Boolean isDelete;
        public Boolean isUndelete;
        public List<sObject> triggerNew;
        public List<sObject> triggerOld;
        public Map<Id, sObject> newMap;
        public Map<Id, sObject> oldMap;

        public TriggerParams(Boolean isBefore, Boolean isAfter, Boolean isInsert, Boolean isUpdate,
                                            Boolean isDelete, Boolean isUndelete, List<sObject> triggerNew,
                                             List<sObject> triggerOld, Map<Id, sObject> newMap, Map<Id, sObject> oldMap) {
            this.isBefore = isBefore;
            this.isAfter = isAfter; 
            this.isInsert = isInsert;
            this.isUpdate = isUpdate;
            this.isDelete = isDelete; 
            this.isUndelete = isUndelete;
            this.triggerNew = triggerNew;
            this.triggerOld = triggerOld;
            this.newMap = newMap; 
            this.oldMap = oldMap;
        }
    }

    //here all methods should be called
    public static void entry(TriggerParams triggerParams) {
        List<Lead> triggerNew = (List<Lead>)triggerParams.triggerNew;
        String userType = userinfo.getUserType();
        
        if(triggerParams.isBefore){
            if(triggerParams.isInsert){
                if(userType == 'PowerPartner'){ //ab - more info on http://www.salesforce.com/us/developer/docs/api/Content/sforce_api_objects_user.htm 
                    Id userId = userinfo.getUserId();
                    User u = [Select Id, Contact.AccountId from User where Id=:userId];
                    Id partnerAccount = u.Contact.AccountId;
                    for(Lead  l : triggerNew){
                        l.Leadsource__c = partnerAccount;
                        l.LeadSource = 'LeaseCo';
                    }
                }
            }
            if(triggerParams.isUpdate){
          for(Lead l : triggerNew) {
              if (l.IsConverted){
                  system.debug('############## Acc Id -->' + l.ConvertedAccountId);
                  Account acc = [select Id, RecordTypeId, PersonContactId from Account where Id = :l.ConvertedAccountId];
                  system.debug('############## Acc RecordTypeId : ' + acc.RecordTypeId);
                  RecordType rt = [Select DeveloperName From RecordType where Id = :acc.RecordTypeId];
                  system.debug('############## RecordType Name : ' + rt.DeveloperName);
                  //l.ConvertedOpportunityId, l.ConvertedContactId
                  if(rt.DeveloperName == 'PersonAccount'){
                    Opportunity opp = (l.ConvertedOpportunityId != null) ? new Opportunity(id=l.ConvertedOpportunityId): null;
                    
                    acc.Account_manager__c = l.Account_Manager__c;
                    acc.Car_Delivery_Date__pc = l.Car_Delivery_Date__c;
                    acc.Brand_Car__c = l.Brand_Car__c;
                    acc.Car_type__c = l.Type_Car__c;
                    acc.Phone = l.Company_Phone__c;
                    acc.AccountSource = l.LeadSource;
                    
                    acc.just_converted__c = false;
                    
                    update acc;
                    
                    Contact con = (l.ConvertedContactId != null) ? new Contact(id=l.ConvertedContactId): null;
                    con.HomePhone = l.Phone;
                    con.MobilePhone = l.MobilePhone;
                    update con;  
                    
                    opp.Send_Quote_To__c = (l.Account_Manager__c != null) ? l.Account_Manager__c : Acc.PersonContactId;
                     opp.Leadsource__c = l.Leadsource__c;
                    opp.LeadSource = l.LeadSource;
                    update opp;
                    
                  }
                  else if(rt.DeveloperName == 'Business_Account'){
                    Opportunity opp = (l.ConvertedOpportunityId != null) ? new Opportunity(id=l.ConvertedOpportunityId): null;
                    Contact con = (l.ConvertedContactId != null) ? new Contact(id=l.ConvertedContactId): null;
                    
                    acc.Phone = l.Company_Phone__c;
                    acc.Account_manager__c = l.Account_Manager__c;
                    acc.Leadsource__c = l.Leadsource__c;
                    acc.AccountSource = l.LeadSource;
                    acc.ParentId = l.Parent_Account__c;

                    acc.ShippingStreet = l.street;
                    acc.ShippingCity = l.City;
                    acc.ShippingState = l.State;
                    acc.ShippingCountry = l.Country;
                    acc.ShippingPostalcode = l.PostalCode;
                    
                    acc.just_converted__c = false;
                                        
                    update acc;
                    
                    opp.Send_Quote_To__c = (l.Account_Manager__c != null) ? l.Account_Manager__c : null;
                    opp.Leadsource__c = l.Leadsource__c;
                    opp.LeadSource = l.LeadSource;
                    update opp;
                    
                    con.Phone = l.Phone;
                    update con;
                  }
                  else if(rt.DeveloperName == 'Partner_Account'){
                  
                  }
              }
          }
      }
        }
    }
}


Thanks in advance!