C# Academy · Lesson

Guarding Against Nulls

Validation and patterns.

Why Guard Against Nulls?

A method that receives an unexpected null often crashes later with a confusing NullReferenceException deep in the call stack.

Guarding means checking arguments up front and failing clearly, so the error points straight at the real cause.

The simplest guard is an explicit check that throws an ArgumentNullException when a required argument is null.

This validates input at the boundary of your method, before any work begins.

void Save(string path)
{
    if (path == null)
        throw new System.ArgumentNullException(nameof(path));
    System.Console.WriteLine(path);
}