Do not returns null

If you create a method that return a list and you don’t have data, always return empty list instead of null. This would allow the caller to iterate the list without checking. As an example, consider the 2 blocks of code below, which is better?

var customers = GetCustomers();
foreach(var customer in customers) {
  // do something
}

var customers = GetCustomers();
if (customers != null) {
  foreach(var customer in customers) {
    // do something
  }
}

Having said that, if you write caller side code and received a list. Make sure you don’t get NullReferenceException by using this code.

var customers = GetCustomers();
foreach(var customer in customers ?? Array.Empty<Customer>()) {
  // do something
}