Null Checking Patterns

Null checking is an essential part of writing robust C# code. There are several patterns you can use to check for null values safely.

Let's explore some common null checking patterns:

First, the basic if-null check:

string name = null;

if (name == null)
{
    Console.WriteLine("Name is null");
}

Another common pattern is the null-conditional operator (?.), which safely accesses members of potentially null objects:

string name = null;
int? length = name?.Length;  // length will be null

The null-coalescing operator (??) provides a default value when an expression is null:

string name = null;
string displayName = name ?? "Unknown";  // displayName will be "Unknown"

You can also chain these patterns for more complex scenarios:

string name = null;
int length = (name ?? "").Length;  // length will be 0

The string.IsNullOrWhiteSpace() method checks whether a string is null, empty, or contains only whitespace characters. It is a convenient way to validate string input in a single call:

string name = null;

if (string.IsNullOrWhiteSpace(name))
{
    Console.WriteLine("No name provided");  // this will print
}

string blank = "   ";

if (string.IsNullOrWhiteSpace(blank))
{
    Console.WriteLine("Blank name provided");  // this will also print
}

Use string.IsNullOrWhiteSpace() when you want to treat null, empty strings, and whitespace-only strings as equivalent invalid input.