How to use Fluent Assertions to test for exception in inequality tests?

I'm trying to write a unit test for a greater than overridden operator using Fluent Assertions in C#. The greater than operator in this class is supposed to throw an exception if either of the objects are null.

Usually when using Fluent Assertions, I would use a lambda expression to put the method into an action. I would then run the action and use action.ShouldThrow<Exception>. However, I can't figure out how to put an operator into a lambda expression.

I would rather not use NUnit's Assert.Throws(), the Throws Constraint, or the [ExpectedException] attribute for consistencies sake.