Hello everyone, i have the following trigger test class. When i run the test I get the System.NullPointerException: Attempt to de-reference a null object error in line 59,
@isTest
private class accountNameDupePreventer {

    static testMethod void myUnitTest() {
        // TO DO: implement unit test
        Test.startTest();
        // First make sure there are no accounts already in the system
        // that have the Accounts used for testing
        Set<String> testAccountNames = new Set<String>();
        testAccountNames.add('Test1Dup Inc.');
        testAccountNames.add('Test2Dup Inc.');
        testAccountNames.add('Test3Dup Inc.');
        System.assert([SELECT count() FROM Account WHERE Name IN :testAccountNames] == 0);
    
        // Seed the database with some accounts, and make sure they can be bulk inserted successfully.
        Account account1 = new Account(Name = 'Test1Dup Inc.', BillingCountry = 'United States', BillingState = 'Texas');
        Account account2 = new Account(Name = 'Test4Dup Inc.', BillingCountry = 'United States', BillingState = 'California');
        Account account3 = new Account(Name = 'Test5Dup Inc.', BillingCountry = 'United States', BillingState = 'Florida');
        Account[] accts = new Account[] { account1, account2, account3 };
        insert accts;
        
        // Now make sure that some of these accounts can be changed and
        // then bulk updated successfully. Note that account1 is not
        // being changed, but is still being passed to the update
        // call. This should be OK.
        account2.Name = 'Test2Dup Inc.';
        account3.Name = 'Test3Dup Inc.';
        update accts;
        
        // Make sure that single row account duplication prevention works on insert.
        Account dup1 = new Account(Name='Test1Dup Inc.', BillingCountry = 'United States');
        try {
            insert dup1;
            System.assert(false);
        } catch (DmlException e) {
            System.assert(e.getNumDml() == 1);
            System.assert(e.getDmlIndex(0) == 0);
            System.assert(e.getDmlFields(0).size() == 1);
            System.assert(e.getDmlFields(0)[0] == Account.Name);
            System.assert(e.getDmlMessage(0).indexOf(
            'An account with this account\'s name already exists.') > -1);
        }
        
        // Make sure that single row account duplication prevention works on update.
        dup1 = new Account(Id=account1.Id, Name='Test3Dup Inc.', BillingCountry = 'United States');
        try {
            update dup1;
            System.assert(false);
        } catch (DmlException e) {
            System.assert(e.getNumDml() == 1);
            System.assert(e.getDmlIndex(0) == 0);
            System.assert(e.getDmlFields(0).size() == 1);
            System.assert(e.getDmlFields(0)[0] == Account.Name);
            System.assert(e.getDmlMessage(0).indexOf(
            'An account with this account\'s name already exists.') > -1);
        }
        
        // Make sure that bulk account duplication prevention works on
        // insert. Note that the first item being inserted is fine,
        // but the second and third items are duplicates. Note also
        // that since at least one record insert fails, the entire
        // transaction will be rolled back.
        dup1 = new Account(Name='Test4Dup Inc.', BillingCountry = 'United States');
        Account dup2 = new Account(Name='Test2Dup Inc.', BillingCountry = 'United States');
        Account dup3 = new Account(Name='Test3Dup Inc.', BillingCountry = 'United States');
        Account[] dups = new Account[] {dup1, dup2, dup3};
        try {
            insert dups;
            System.assert(false);
        } catch (DmlException e) {
            // Num=2 because dup1 not fails
            System.assert(e.getNumDml() == 2);
            // dup2 fails
            System.assert(e.getDmlIndex(0) == 1);
            System.assert(e.getDmlFields(0).size() == 1);
            System.assert(e.getDmlFields(0)[0] == Account.Name);
            System.assert(e.getDmlMessage(0).indexOf(
            'An account with this account\'s name already exists.') > -1);
            // dup3 fails
            System.assert(e.getDmlIndex(1) == 2);
            System.assert(e.getDmlFields(1).size() == 1);
            System.assert(e.getDmlFields(1)[0] == Account.Name);
            System.assert(e.getDmlMessage(1).indexOf(
            'An account with this account\'s name already exists.') > -1);
        }
        
        // Make sure that bulk account duplication prevention works on
        // update. Note that the first item being updated is fine,
        // because the name is new, and the second item is
        // also fine, but in this case it's because the 
        // name doesn't change. The third case is flagged as an
        // error because it is a duplicate of the name of the
        // first account's value in the database, even though that value
        // is changing in this same update call. It would be an
        // interesting exercise to rewrite the trigger to allow this
        // case. Note also that since at least one record update
        // fails, the entire transaction will be rolled back.
        dup1 = new Account(Id=account1.id, Name='Test5Dup Inc.', BillingCountry = 'United States');
        dup2 = new Account(Id=account2.id, Name='Test2Dup Inc.', BillingCountry = 'United States');
        dup3 = new Account(Id=account3.id, Name='Test1Dup Inc.', BillingCountry = 'United States');
        dups = new Account[] {dup1, dup2, dup3};
        try {
            update dups;
            System.assert(false);
        } catch (DmlException e) {
            System.debug(e.getNumDml());
            System.debug(e.getDmlMessage(0));
            System.assert(e.getNumDml() == 1);
            System.assert(e.getDmlIndex(0) == 2);
            System.assert(e.getDmlFields(0).size() == 1);
            System.assert(e.getDmlFields(0)[0] == Account.Name);
            System.assert(e.getDmlMessage(0).indexOf(
            'An account with this account\'s name already exists.') > -1);
        }
        
        // Make sure that duplicates in the submission are caught when
        // inserting accounts. Note that this test also catches an
        // attempt to insert an account where there is an existing
        // duplicate.
        dup1 = new Account(Name='Test4Dup Inc.', BillingCountry = 'United States');
        dup2 = new Account(Name='Test4Dup Inc.', BillingCountry = 'United States');
        dup3 = new Account(Name='Test3Dup Inc.', BillingCountry = 'United States');
        dups = new Account[] {dup1, dup2, dup3};
        try {
                insert dups;
                System.assert(false);
        } catch (DmlException e) {
            System.assert(e.getNumDml() == 2);
            System.assert(e.getDmlIndex(0) == 1);
            System.assert(e.getDmlFields(0).size() == 1);
            System.assert(e.getDmlFields(0)[0] == Account.Name);
            System.assert(e.getDmlMessage(0).indexOf(
            'Another inserted/updated account from bulk operation has the same name.') > -1);
            System.assert(e.getDmlIndex(1) == 2);
            System.assert(e.getDmlFields(1).size() == 1);
            System.assert(e.getDmlFields(1)[0] == Account.Name);
            System.assert(e.getDmlMessage(1).indexOf(
            'An account with this account\'s name already exists.') > -1);
        }
        
        // Make sure that duplicates in the submission are caught when
        // updating accounts. Note that this test also catches an attempt
        // to update an account where there is an existing duplicate.
        dup1 = new Account(Id=account1.id, Name='Test4Dup Inc.', BillingCountry = 'United States');
        dup2 = new Account(Id=account2.id, Name='Test4Dup Inc.', BillingCountry = 'United States');
        dup3 = new Account(Id=account3.id, Name='Test2Dup Inc.', BillingCountry = 'United States');
        dups = new Account[] {dup1, dup2, dup3};
        try {
            update dups;
            System.assert(false);
        } catch (DmlException e) {
            System.assert(e.getNumDml() == 2);
            System.assert(e.getDmlIndex(0) == 1);
            System.assert(e.getDmlFields(0).size() == 1);
            System.assert(e.getDmlFields(0)[0] == Account.Name);
            System.assert(e.getDmlMessage(0).indexOf(
            'Another inserted/updated account from bulk operation has the same name.') > -1);
            System.assert(e.getDmlIndex(1) == 2);
            System.assert(e.getDmlFields(1).size() == 1);
            System.assert(e.getDmlFields(1)[0] == Account.Name);
            System.assert(e.getDmlMessage(1).indexOf(
            'An account with this account\'s name already exists.') > -1);
        }
        Test.stopTest();
    }
}

"System.assert(e.getDmlFields(0).size() == 1);", the error is thrown in this line. Can anyone tell me how to solve this?
ThanksinAdvance!