Description of exception Abstract Class WhenCalled Equals

    public abstract class BaseClass
    {

    
    }

        [Test]
        public void EqualsCall()
        {
            var baseClass = Isolate.Fake.Instance<BaseClass>();
            Isolate.WhenCalled(()=>baseClass.Equals(null)).CallOriginal();
        }

failed: TypeMock.TypeMockException :
*** No method calls found in recording block. Please check:
* Are you trying to fake a field instead of a property?
* Are you are trying to fake mscorlib type?
at f4.a(ci A_0, Boolean A_1)
at da.a(Boolean A_0)
at de.b(Boolean A_0)
at ic.c(Boolean A_0)
at ic.a(Object A_0, Boolean A_1, Func`1 A_2, Action A_3, Action A_4, Action A_5)
at ic.a(Object A_0, Boolean A_1, Action A_2, Action A_3)
at ic.CallOriginal()