Coding style – confusion with Uncle Bob About Null Objects in Cleaning Codes in Cleaning Codes

public void SendMessage(IEmailSender emailSender, contactList list)
{
 if(emailSender == null)
 {
 throw new ArgumentNullException("Failed to send 
 message.",MethodBase.GetCurrentMethod().GetParameters[0].Name);
 }
 if(list == null)
 {
 throw new ArgumentNullException("Failed to send 
 message.",MethodBase.GetCurrentMethod().GetParameters[1].Name);
 }

 // rest of code goes here

}

if(log != null)
 log. Write("My log message");

I am reading today Uncle Bob’s book on exception handling, and what I can recall from handling null values ​​is that methods should not handle null values, because it will mess up the code. I am a bit confused.
I always think that a method should always ensure Its dependencies are not null (unless they inject nullability in the constructor and the constructor).
For example, if I have a method

 public void SendMessage(IEmailSender emailSender, contactList list)
{
 if(emailSender == null)
 {
 throw new ArgumentNullException("Failed to send 
 message." ,MethodBase.GetCurrentMethod().GetParameters[0].Name);
 }
 if(list == null)
 {
 throw new ArgumentNullException("Failed to send 
 message.",MethodBase.GetCurrentMethod().GetParameters[1].Name );
 }

 // rest of code goes here

}

Am I missing something?

I haven’t read this book yet, but I can only imagine Uncle Bob who advocates using the Null Object Pattern in preference to explicit null reference handling.

For example, instead of

if(log != null)
 log.Write("My log message");

You can instead create an ILogger interface that contains the Write method, and create two classes that implement this interface: NullLogger and FileLogger. NullLogger will provide an empty body for the implementation of the Write method.

In my opinion, this is different from your explicit precondition verification in your example