We'd need to see more code to know for sure, but it looks like newCustomer.getMyAccount() is null. You check that newCustomer itself isn't null. But not that its account isn't null. So then getting the account number has the possibility of a NullPointer.
You cannot expect an instructor to do everything for you.
I believe that you should write a constructor for every class you write. And that every constructor should initialise every instance field to a sensible value. Having sensible value for all instance fields is called having your object in a consistent state.
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