Right now we have no way to query the presence of fields or not in queries written with EF.

This just requires detecting them and opting them out of partial evaluation via an implementation of EvaluationExpressionFilter.

Would also recommend overloads for these methods be added to the C# Driver to allow syntax like Customers.Where(c => Mql.IsMissing("Address")) etc. to support shadow properties. If aggreed, that will need a ticket on the driver and should be written independently to not rely on EF.