Nullable

string nonNullable = "Hello, World!"; // Non-nullable reference type 

string? nullableString = null; // Nullable reference type 

// Define as non-nullable, but tell compiler to ignore warning (Null forgiving)

// Same as FooBar fooBar = default!;

FooBar fooBar = null!;

// Define as non-nullable, assign using 'new' keyword

FooBar fooBar = new(Id: 1, Name: "Foo");

string? nullableMessage = null; 

string message = nullableMessage ?? "Default message"; 

// or

private IPersonReader? reader;

public IPersonReader Reader

{

get => reader ??= new PersonReader();

set => reader = value;

I}

Using Nullability and Null Operators 

string? input = null; 

// If input is null, length becomes 0; otherwise, it gets the length of the string. 

int? length = input?.Length ?? 0; 

Console.WriteLine(length); // Output: 0