How do I setup a mock that returns IHttpActionResult?

I'm using VisualStudio 2015, .NET 4.6, Moq 4.5.2, Nunit 3.4.1 to test a WebApi2 Controller. However, I am getting a null response object when mocking the intended controller method:

var response = actionResult as NegotiatedContentResult;

I am guessing I must be setting up my mock of the UserService incorrectly?

My suspicion is that this part is the culprit:

userServiceMock.Setup(service => service.InsertOrUpdateUser( It.IsAny())).Returns(1);

As I am getting the following in the output window:

'((System.Web.Http.Results.OkNegotiatedContentResult)actionResult).Request' threw an exception of type 'System.InvalidOperationException'

Is the problem that I am telling Moq to expect a return value of 1, but the Put method returns OkNegotiatedContentResult?

My questions are (possibly the same question):

1) Am I setting up my Moq correctly and

2) how do I resolve the problem so my response object is populated?

Thanks much.

Here is the Test method:

[Test]
public void Put_ShouldUpdate_User()
{
    // Arrange
    var userServiceMock = new Mock<IUserService>();

    userServiceMock.Setup(service => service.InsertOrUpdateUser(
        It.IsAny<User>())).Returns(1);

    var controller = new UsersController(userServiceMock.Object);

    // Act
    IHttpActionResult actionResult = controller.Put(

        new User()
        {
            Id = 1,
            Name = "Joe"
        });

    var response = actionResult as NegotiatedContentResult<User>;

    // Assert:
    Assert.IsNotNull(response);
    var newUser = response.Content;
    Assert.AreEqual(1, newUser.Id);
    Assert.AreEqual("Joe", newUser.Name);
}

Here is the UserController method:

// PUT api/users/1
public IHttpActionResult Put(User user)
{
    if (!ModelState.IsValid)
    {
        return BadRequest(ModelState);
    }

    return Ok(_userService.InsertOrUpdateUser(user));

}

Finally, the method for the UserService:

public int InsertOrUpdateUser(User user)
{
    return _userRepository.InsertOrUpdateUser(user);
}