How to Check for Null in C# (is null, ?., ??, Empty Objects)

The usual way to check for null in C#, if (order == null), once skipped real orders in a client’s checkout. Their Order class overloaded ==, so an empty cart compared equal to null.

Quick answer: write order is null or order is not null. The compiler never calls an overloaded operator for those patterns.

I ran every check below on .NET 10, from ?. and ??= to empty lists, custom objects and C# 14’s null-conditional assignment.

Why == null Can Lie: Check for Null with is null

Here’s that bug, cut down. The == operator compares item counts and counts null as 0 items:

Order emptyCart = new(0);

Console.WriteLine($"emptyCart == null: {emptyCart == null}");
Console.WriteLine($"emptyCart is null: {emptyCart is null}");
Console.WriteLine($"ReferenceEquals:   {ReferenceEquals(emptyCart, null)}");

class Order(int items)
{
    public int Items { get; } = items;
    // "equal" when item counts match, and null counts as 0 items
    public static bool operator ==(Order? a, Order? b)
        => (a?.Items ?? 0) == (b?.Items ?? 0);
    public static bool operator !=(Order? a, Order? b) => !(a == b);
    public override bool Equals(object? o) => o is Order x && x.Items == Items;
    public override int GetHashCode() => Items;
}

Output:

emptyCart == null: True
emptyCart is null: False
ReferenceEquals:   False

emptyCart == null prints True for an object that exists, while is null and ReferenceEquals compare the reference itself. That’s why Microsoft’s IDE0041 style rule suggests is null.

is not null, == null and is { }: The Basic Null Checks

Here’s a lookup that returns a name or null, the way most C# functions that search for something do:

string? FindCustomer(int id) => id == 1 ? "Jenna Morales" : null;

if (FindCustomer(2) is null) Console.WriteLine("Customer 2: not found");
if (FindCustomer(1) is { } name) Console.WriteLine($"Found: {name}");

Output:

Customer 2: not found
Found: Jenna Morales

is { } name checks for null and copies the value into a non-null variable. is not null (C# 9+) is the plain negation, and == null is fine for string.

Plain value types like int can’t hold null at all, as the C# data types guide explains.

Null-Conditional ?. and Null-Coalescing ?? Operators

Often you don’t want an if at all, just a safe read with a fallback. Here’s a customer with an optional city:

Customer jenna = new("Jenna Morales", null);
Customer? guest = null;

Console.WriteLine(jenna.City ?? "(no city)");
Console.WriteLine(guest?.Name ?? "(guest)");
Console.WriteLine(guest?.Name.Length ?? 0);

jenna.City ??= "Austin, TX";        // assigns only when City is null
Console.WriteLine(jenna.City);

guest?.City = "Dallas, TX";         // C# 14: skipped, no exception
jenna?.City = "Houston, TX";
Console.WriteLine($"{jenna?.City} | guest is null: {guest is null}");

class Customer(string name, string? city)
{
    public string Name { get; } = name;
    public string? City { get; set; } = city;
}

Output:

(no city)
(guest)
0
Austin, TX
Houston, TX | guest is null: True

guest?.Name.Length ?? 0 prints 0 because the whole chain stops at the null guest. guest?.City = ... is C# 14’s null-conditional assignment: it runs only for a non-null object.

My C# 14 new features roundup covers the rest. Compound forms like ?.Total += work too, but ++ and -- don’t.

Throw Early with ArgumentNullException.ThrowIfNull

When null means a caller bug, don’t hide it with a default. One line replaces the old if (x == null) throw block:

try
{
    Ship(null);
}
catch (ArgumentNullException ex)
{
    Console.WriteLine(ex.Message);
}
Ship("Tyler Brooks");

static void Ship(string? customer)
{
    ArgumentNullException.ThrowIfNull(customer);
    Console.WriteLine($"Shipping to {customer}");
}

Output:

Value cannot be null. (Parameter 'customer')
Shipping to Tyler Brooks

ThrowIfNull (.NET 6+) fills in the parameter name for you. Catch it where you can report the problem, as shown in my try-catch in C# guide.

How Do You Check a Nullable int (int?) for Null?

An int can’t be null, but int? can. A survey rating the customer skipped is a good fit:

int? rating = null;     // customer skipped the survey

Console.WriteLine($"rating.HasValue: {rating.HasValue}");
Console.WriteLine($"rating is null:  {rating is null}");
Console.WriteLine($"GetValueOrDefault: {rating.GetValueOrDefault()}");
Console.WriteLine($"rating ?? 5: {rating ?? 5}");

Output:

rating.HasValue: False
rating is null:  True
GetValueOrDefault: 0
rating ?? 5: 5

HasValue and is null agree, and reading rating.Value while it’s null throws InvalidOperationException. For more, see how to convert null to int in C#.

Nullable Reference Types: Let the Compiler Find Missing Null Checks

File-based apps and new .NET 10 projects turn on nullable reference types. When you declare variables in C# as string?, the compiler warns on unchecked use:

string? coupon = FindCoupon("TX");
Console.WriteLine(coupon.ToUpper());     // warning CS8602

string? FindCoupon(string state) => state == "CA" ? "fall26" : null;

Build and run output:

C:\DotNetDemo\NullCheckDemo\NullableWarning.cs(2,19): warning CS8602: Dereference of a possibly null reference.
Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
   at Program.<Main>$(String[] args) in C:\DotNetDemo\NullCheckDemo\NullableWarning.cs:line 2

CS8602 is only a warning, so the program still ran and crashed (and coupon! would only hide it). The fix is coupon?.ToUpper() ?? "NONE" or an is not null check.

Check if a List or Array Is Null or Empty

Collections have two failure states: no list at all, or a list with nothing in it. One pattern covers both for a List in C#:

List<string>? noCart = null;
List<string> emptyCart = [];
string[] cart = ["Hiking boots", "Rain jacket"];

Show("noCart null or empty", noCart is null or { Count: 0 });
Show("emptyCart null or empty", emptyCart is null or { Count: 0 });
Show("noCart?.Any() != true", noCart?.Any() != true);
Show("emptyCart is []", emptyCart is []);
Show("noCart is []", noCart is []);
Show("cart is [_, ..]", cart is [_, ..]);

static void Show(string label, bool value) => Console.WriteLine($"{label,-24}{value}");

Output:

noCart null or empty    True
emptyCart null or empty True
noCart?.Any() != true   True
emptyCart is []         True
noCart is []            False
cart is [_, ..]         True

Watch the noCart is [] line: it prints False, because a list pattern never matches null. Use is null or [] if you want both.

Arrays use is null or { Length: 0 }. A Dictionary in C# has Count, so the list version works unchanged.

How to Check if a Custom Object Is Null or Empty

C# has no built-in “empty” for your own classes, so you define it, a small piece of encapsulation in C#. I call an address empty when street and city are blank:

Address blank = new();
Address home = new() { Street = "418 Oak Ave", City = "Austin" };
Address? none = null;

Console.WriteLine($"blank.IsEmpty: {blank.IsEmpty}");
Console.WriteLine($"home.IsEmpty:  {home.IsEmpty}");
Console.WriteLine($"none?.IsEmpty ?? true: {none?.IsEmpty ?? true}");
Console.WriteLine($"blank == new(): {blank == new Address()}");

record Address
{
    public string? Street { get; init; }
    public string? City { get; init; }
    public bool IsEmpty =>
        string.IsNullOrWhiteSpace(Street) && string.IsNullOrWhiteSpace(City);
}

Output:

blank.IsEmpty: True
home.IsEmpty:  False
none?.IsEmpty ?? true: True
blank == new(): True

none?.IsEmpty ?? true is the null-or-empty check in one expression. Because Address is a record, blank == new Address() also works, since records compare values.

Strings: Use IsNullOrEmpty or IsNullOrWhiteSpace

Strings get their own helpers: string.IsNullOrEmpty and string.IsNullOrWhiteSpace, which also rejects text like three spaces. I’ve covered both with real inputs in how to check if a string is not null or empty in C#.

Common Null Check Errors and How to Fix Them

Three mistakes I still see in code reviews, run so you can see what each one throws:

string? promo = null;
List<int>? orders = null;

Try("promo!.Equals(null)", () => promo!.Equals(null));
Try("orders!.Any()", () => orders!.Any());
Try("orders!.Count", () => orders!.Count);

static void Try(string label, Func<object> run)
{
    try { Console.WriteLine($"{label}: {run()}"); }
    catch (Exception ex) { Console.WriteLine($"{label}: {ex.GetType().Name}"); }
}

Output:

promo!.Equals(null): NullReferenceException
orders!.Any(): ArgumentNullException
orders!.Count: NullReferenceException

Mistake	What happens	Fix
promo.Equals(null)	NullReferenceException	promo is null
orders.Any() on a null list	ArgumentNullException	orders is null or { Count: 0 }
orders.Count on a null list	NullReferenceException	orders?.Count ?? 0
count is null on an int	Build error CS0037	Declare it as int?

Which Null Check Should You Use in C#?

Situation	Use
Is it null?	x is null / x is not null
Read a member or use a default	x?.Member ?? fallback
Fill in a missing value	x ??= value
Null is a bug	ArgumentNullException.ThrowIfNull(x)
int?, decimal?	HasValue or ??
List or array	is null or { Count: 0 }
Your own class	An IsEmpty property + ?.IsEmpty ?? true

A few related tutorials pick up where this one stops:

• Type casting in C#, including as and is
• Switch case and pattern matching in C#
• Arrays in C#, from declaration to Length
• C# interview questions for freshers

Frequently Asked Questions