Moq throwing NullReferenceException on Verify with It.Is but not It.IsAny

Question

Running the unit tests against my latest build I got an unexpected failure. It was odd because the test was against code I hadn't changed. The test looks something like this:

[Fact]
public void My_Test()
{
    // Arrange
    var expectedValuation = new Money { Amount = 0, Currency = "GBP" };

    this.mockMoneyConverter.Setup(x => x.Convert(It.IsAny<MoneyWorks.Money>(), It.IsAny<Money>(), It.IsAny<ResolutionContext>()))
        .Returns(expectedValuation);

    var input = new QueryResults.ExistingItemResult
    {
        Balances = null
    };

    // Act
    var actual = this.target.Map<ExistingItemSummary>(input);

    // Assert
    actual.Valuation.ShouldBe(expectedValuation);

    this.mockMoneyConverter.Verify(x => x.Convert(It.Is<MoneyWorks.Money>(money => money.Amount == 0), It.IsAny<Money>(), It.IsAny<ResolutionContext>()));
}

The ShouldBe passes fine but the Verify throws an error:

 Message: 
    System.NullReferenceException : Object reference not set to an instance of an object.
lambda_method(Closure , Money )
    <>c__DisplayClass2_0`1.<Is>b__0(TValue value)
    Match`1.Matches(Object value)
    Matcher.Matches(Object value)
    MethodCall.Matches(ICallContext call)
    <>c__DisplayClass56_0.<VerifyCalls>b__0(ICallContext ac)
    WhereListIterator`1.MoveNext()
    Enumerable.Count[TSource](IEnumerable`1 source)
    Mock.VerifyCalls(Interceptor targetInterceptor, MethodCall expected, Expression expression, Times times)
    Mock.Verify[T,TResult](Mock`1 mock, Expression`1 expression, Times times, String failMessage)
    Mock`1.Verify[TResult](Expression`1 expression)

What I find peculiar is that if I replace the Verify with a genric It.IsAny check, it works and passes:

this.mockMoneyConverter.Verify(x => x.Convert(It.IsAny<MoneyWorks.Money>(), It.IsAny<Money>(), It.IsAny<ResolutionContext>()));

Is there any reason why the original It.Is check should start to fail all of a sudden?

Answer 1

money.Amount == 0

If money is null, it won't be able to evaluate this and I'd expect a null reference exception.

Changing it to handle the null case should sort it out if that's your issue

It.Is<MoneyWorks.Money>(money => money != null && money.Amount == 0)