What does exclamation mark mean before invoking a method in C# 8.0?

I have found a code written in C# seemingly version 8.0. In the code, there is an exclamation mark before invoking a method. What does this part of the code mean, and above all, what are its uses?

var foo = Entity!.DoSomething();

This would be the null forgiving operator.
It tells the compiler "this isn't null, trust me", so it does not issue a warning for a possible null reference.

In this particular case it tells the compiler that Entity isn't null.

! is the Null-Forgiving Operator. To be specific it has two main effects:

• it changes the type of the expression (in this case it modifies Entity) from a nullable type into a non-nullable type; (for example, object? becomes object)

• it suppresses nullability related warnings, which can hide other conversions

This seems to come up particularly with type parameters:

IEnumerable<object?>? maybeListOfMaybeItems = new object[] { 1, 2, 3 };

// inferred as IEnumerable<object?>
var listOfMaybeItems = maybeListOfMaybeItems!;

// no warning given, because ! supresses nullability warnings
IEnumerable<object> listOfItems = maybeListOfMaybeItems!;

// warning about the generic type change, since this line does not have !
IEnumerable<object> listOfItems2 = listOfMaybeItems;

This is called the null-forgiving operator and is available in C# 8.0 and later. It has no effect at run time, only at compile time. It's purpose is to inform the compiler that some expression of a nullable type isn't null to avoid possible warnings about null references.

In this case it tells the compiler that Entity isn't null.