Hi All,
I'm new to salesforce and started working on Trailhead's. I facing issue with the Trigger Challenge. Here is the triger code im writing 

trigger AccountAddressTrigger on Account (before insert) {
    for(Account a : Trigger.new){
        if(a.Match_Billing_Address__c && a.BillingPostalCode != null){
            a.ShippingPostalCode = a.BillingPostalCode;
        }
    }
    
}

but i'm getting the following error. Not sure where i'm doing wrong. can someone please help me here. Thanks in advance.

System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, TestTrigger: execution of AfterInsert caused by: System.NullPointerException: Attempt to de-reference a null object Trigger.TestTrigger: line 3, column 1: []

public class ContactAndLeadSearch {
public static List<List<SObject>> searchContactsAndLeads(string FN)
{
    List<List<sObject>> searchList = [FIND 'FN' IN all fields 
RETURNING Contact(FirstName,LastName) ,Lead(FirstName,Lastname)];
//Contact[] searchContacts = (Contact[])searchList[0];
//Lead[] searchLeads = (Lead[])searchList[1];
return searchList;
   

}
}

Please someone correct this code ,, this one was nt fulfilling the challenge req.

Hi,
I am not able to understand the below question correctly Please help me out. - 
Create a class that has a method accepting two strings. The method searches for contacts that have a last name matching the first string and a mailing postal code (API name: MailingPostalCode) matching the second. It gets the ID and Name of those contacts and returns them.The Apex class must be called 'ContactSearch' and be in the public scope.
The Apex class must have a public static method called 'searchForContacts'.
The 'searchForContacts' method must accept two incoming strings as parameters, find any contact that has a last name matching the first, and mailing postal code matching the second string. The method should return a list of Contact records with at least the ID and Name fields.
The return type for 'searchForContacts' must be 'List<Contact>'.