A *throw expression* throws the value produced by evaluating the *null_coalescing_expression*, which must denote a value of the class type `System.Exception`, of a class type that derives from `System.Exception` or of a type parameter type that has `System.Exception` (or a subclass thereof) as its effective base class. If evaluation of the expression produces `null`, a `System.NullReferenceException` is thrown instead.
The behavior at runtime of the evaluation of a *throw expression* is the same [as specified for a *throw statement*](https://github.com/dotnet/csharplang/blob/master/spec/statements.md#the-throw-statement).
- For every variable *v*, *v* is definitely assigned before the *null_coalescing_expression* of a *throw_expression* iff it is definitely assigned before the *throw_expression*.
- For every variable *v*, *v* is definitely assigned after *throw_expression*.
A *throw expression* is permitted in only the following syntactic contexts:
- As the second or third operand of a ternary conditional operator `?:`
- As the second operand of a null coalescing operator `??`
- As the body of an expression-bodied lambda or method.