/errors /csharp/cs8618-non-nullable-property-must-contain-non-null-value

C# warning CS8618: Non-nullable property must contain a non-null value when exiting constructor

updated 2026-10-21

tool: C#
exit code: 0
versions: C# 8+ with nullable reference types, .NET 6 – 10 (enabled by default in new projects)
os: any

warning CS8618: Non-nullable property 'Name' must contain a non-null value when exiting constructor comes from C# nullable reference types. The property is declared as string (meaning "never null"), but after the constructor finishes nothing has assigned it, so it is still null. Mark it required, give it an initial value, set it in the constructor, or declare it string? if null is allowed.

Reproduce it

bash

dotnet new console -o app >/dev/null 2>&1
cd app
cat > Program.cs <<'EOF'
var u = new User { Name = "Ada" };
Console.WriteLine(u.Name);

class User
{
    public string Name { get; set; }
}
EOF
dotnet build -nologo 2>&1 | grep -o 'warning CS8618: [^[]*' | sort -u

Output

warning CS8618: Non-nullable property 'Name' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

The build succeeds: CS8618 is a warning. Projects with <TreatWarningsAsErrors>true</TreatWarningsAsErrors> (or <WarningsAsErrors>nullable</WarningsAsErrors>) turn it into error CS8618 and the build fails.

Fix: required, initializer, constructor or nullable

bash

dotnet new console -o app >/dev/null 2>&1
cd app
cat > Program.cs <<'EOF'
var u = new User { Name = "Ada" };
var o = new Order("A-1");
Console.WriteLine($"{u.Name} {u.Email.Length} {o.Id} {u.Nickname ?? "(none)"}");

class User
{
    public required string Name { get; set; }       // callers must set it
    public string Email { get; set; } = string.Empty; // default value
    public string? Nickname { get; set; }           // null is allowed
}

class Order(string id)                               // primary constructor (C# 12)
{
    public string Id { get; } = id;
}
EOF
dotnet build -nologo 2>&1 | grep -c 'CS8618'
dotnet run --no-build

Output

0
Ada 0 A-1 (none)

Fix	Use when
required string Name	The caller must always provide the value (C# 11+)
string Name = string.Empty	An empty value is a sensible default
Assign in the constructor	The value is a constructor argument
string? Name	The value is genuinely optional
string Name = null!	A framework sets it later; silences the warning without any check

Sources

errors · csharpC# error CS0246: The type or namespace name could not be foundCS0246 means the C# compiler cannot resolve a type or namespace: a missing using directive, NuGet package or project reference. Real dotnet build output.commands · dotnet-clidotnet new console: create and run a C# console appdotnet new console -o MyApp creates a C# console project with top-level statements, and dotnet run builds and starts it. Options and other common templates.errors · dotnet-clierror NETSDK1045: The current .NET SDK does not support targeting .NET XNETSDK1045 means the project's TargetFramework is newer than the installed .NET SDK supports. Install a newer SDK, fix global.json, or lower TargetFramework.flags · csharpC# Nullable=enable (dotnet build -p:Nullable): nullable reference type warningsC# Nullable=enable turns on nullable reference type warnings like CS8602 and CS8618. The four values enable, warnings, annotations, disable, and how to migrate.

Reproduce it

Fix: required, initializer, constructor or nullable

Sources

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