When the call looks like:

var result = new PersistenceSpecification<EntityRevision>(this.Session)
    .CheckReference(x=> x.Entity, entity);

error CS0121: The call is ambiguous between the following methods or properties: 'PersistenceSpecificationExtensions.CheckReference<T, TReference>(PersistenceSpecification, Expression<Func<T, TReference>>, TReference)' and 'PersistenceSpecificationExtensions.CheckReference<T, TReference>(PersistenceSpecification, Expression<Func<T, object>>, TReference, params Func<TReference, object>[])'

Adding , (IEqualityComparer) null as a parameter fixes the resolution, but isn't ideal.

Visual Studio 2015, C# 6.0, .NET 4.7.2