What is wrong with my code?

Description: The purpose of this code is to create multiple records based on two conditions

1. Custom Picklist: Value = Yes (condition set in process builder)
2. (Number Field) Contract Term (Number of years) =

So whatever is the value entered in the contract term custom field, those many child record would be created.
Parent Object: Opportunity Contract
Child Object: Annual Maintenance
Error in Production
This code is working fine in Developer Sandbox, after I installed in Production, this program is working as expected with the opportunity contract records which were previously created (before deploying this code)
However, this code does not work with opportunity contract records which are created after the deployment.
The error I am geting is “dereference a null object”
Where am I going wrong? Why this behaviour of working for existing records and not working with new records in Production?

Finally i have recomplied all Apex Classes in Production, but the result is the same

Any Help is highly appreciated!

Below is the code
public class OppConAMInvocableClass {
    @InvocableMethod(label='Insert Child Records for Opportunity Contracts' description='Inserts the child records based on number of contract years.')
  public static void insertChildRecords(List<Opportunity_Contract__c> parentList) {
      List<Annual_Maintenance__c> childrecords = new List<Annual_Maintenance__c>();       
      for(Opportunity_Contract__c parent : parentList) {
        Integer numberYears = Integer.valueOf(parent.Contract_Years__c);
        for(Integer i=1;i<numberYears;i++) {
        //Account acct = [SELECT Id FROM Account where Id = :e.WhatId];
        Integer j = i + 1;         
        Annual_Maintenance__c child = new Annual_Maintenance__c();
           
         
            Child.Anniversary_Date__c=Parent.Annual_Renewal_Date__c.addYears(i); 
            Child.Name=Parent.Name+'-'+Child.Anniversary_Date__c.year();
            Child.Number_of_sites__c=Parent.Number_of_Sites__c;
            Child.Opportunity_Department__c =Parent.Opportunity_Department__c;
            Child.Account__c=Parent.Account_Name__c;
            Child.Primary_Contact__c=Parent.Primary_Contact__c;
            Child.Annual_Maintenance_Start_Date__c=Parent.Contract_Start_Date__c;
            Child.Annual_Maintenance_End_Date__c=Parent.Contract_End_Date__c;
            Child.Opportunity_Name__c=Parent.Opportunity_Name__c;
          Child.Anniversary_Date__c=Parent.Annual_Renewal_Date__c;
            Child.Sales_Territory__c=Parent.Sales_Territory__c;
     Child.Annual_Maintenance_Amount__c=Parent.SMS_Maintenance_Amount__c;
        child.Opportunity_Contract__c=parent.Id;
        childrecords.add(child);
        }
      }   
    Database.SaveResult[] results = Database.insert(childrecords);
    /*
    List<ID> itemIds = new List<ID>();
    for (Database.SaveResult result : results) {
      if (result.isSuccess()) {
        itemIds.add(result.getId());
      }
    }
    return itemIds;
    */
  }
}






 
 

Hi All,

Following is the code for creating multiple child records.

This code is invoked using process builder and condition to satisfy for firing process builder and creating multiple records is choosing value called "Yes" under a picklist called "Approved" on Parent Object which is "Opportunity Contract".

In sandbox this Code is working fine with all custom profiles, when i give them modify all permission for both the custom objects.

In production this code is working for systems administrator alone and not working for other profiles even with modify all permission and i getting following error and not able to save the record for creating multiple child records.

Attempt to de-reference a null object

Here is the code, any suggestions are highly appriciated

public class OppConAMInvocableClass {
    @InvocableMethod(label='Insert Child Records for Opportunity Contracts' description='Inserts the child records based on number of contract years.')
  public static void insertChildRecords(List<Opportunity_Contract__c> parentList) {
      List<Annual_Maintenance__c> childrecords = new List<Annual_Maintenance__c>();        
      for(Opportunity_Contract__c parent : parentList) {
        Integer numberYears = Integer.valueOf(parent.Contract_Years__c);
        for(Integer i=1;i<numberYears;i++) {
        //Account acct = [SELECT Id FROM Account where Id = :e.WhatId];
        Integer j = i + 1;          
        Annual_Maintenance__c child = new Annual_Maintenance__c();
            
          
            Child.Anniversary_Date__c=Parent.Annual_Renewal_Date__c.addYears(i);  
            Child.Name=Parent.Name+'-'+Child.Anniversary_Date__c.year();
            Child.Number_of_sites__c=Parent.Number_of_Sites__c;
            Child.Opportunity_Department__c =Parent.Opportunity_Department__c;
            Child.Account__c=Parent.Account_Name__c;
            Child.Primary_Contact__c=Parent.Primary_Contact__c;
            Child.Annual_Maintenance_Start_Date__c=Parent.Contract_Start_Date__c;
            Child.Annual_Maintenance_End_Date__c=Parent.Contract_End_Date__c;
            Child.Opportunity_Name__c=Parent.Opportunity_Name__c;
            
            //rama
            Child.Anniversary_Date__c=Parent.Annual_Renewal_Date__c;
            Child.Sales_Territory__c=Parent.Sales_Territory__c;
            Child.Annual_Maintenance_Amount__c=Parent.SMS_Maintenance_Amount__c;
        child.Opportunity_Contract__c=parent.Id;
        childrecords.add(child);
        }
      }    
    Database.SaveResult[] results = Database.insert(childrecords);
    /*
    List<ID> itemIds = new List<ID>();
    for (Database.SaveResult result : results) {
      if (result.isSuccess()) {
        itemIds.add(result.getId());
      }
    }
    return itemIds;
    */
  }
}

I need to override the list of recordtypes displaying in the selection panel when the user clicks the "New" button.
Ex: I have recordtype A, B, C in Opportunity, whenever the user clicks "New" the selection window need to display only A and B. But he should have access to C recordtype. Because I have another quick action button in the detail page to create records with C recordtype for the user. 
Is that possible to override the selection window to display specific record type?