Design Patterns: Null Object

Well, let’s start from the beginning! Sir Tony Hoare is who created the null reference, in 1965. Unitl now, Null checks is completly a requirement when we develop something.

Normal Situation

It is usually that we very commom we see null checks, like this:

public void CreateClient(IClient client)
{
    if (client == null) throw new NullReferenceException();
    if (client.Name == null) throw new NullReferenceException();
    // ... do something
}

But, what if you could guarantee that the object was never null?

For this, watch below:

Null Object Pattern

First, we need to define a default object:

public class NullClient : IClient
{
  public int Id => 0;
  public string Name => "Non-client";
  public int Age => 0;
}

Watch that our class inheritance of the IClient interface.

When we do it, we just make this verify:

static void Main(string[] args)
{
    IClient client = new Client();
    var clientService = new ClientService();
    if (client == null)
    	client = new NullClient();
    clientService.CreateClient(client);
}

And when we do the create method, we do not need to verify the object and the name, because we guarantee that the object never is null.

You can see on GitHub.

References

• C# Design Patterns: Null Object | Pluralsight