The following post is more or less a copy-paste of a question I posted on stackoverflow.

My colleagues suggested me to also post a question here on JIRA, so here I am.

I also provided a minimalistic sample code to reproduce the error.

Link to SO: https://stackoverflow.com/questions/51285902/mongodb-c-sharp-driver-2-7-and-serialization-issues

===== ISSUE AND QUESTION ====

I'm currently having a strange issue with the latest mongodb c# driver (2.7), inheritance and serialization.I'm currently having a strange issue with the latest mongodb c# driver (2.7), inheritance and serialization.

Here is a super simplified class hierarchy that I'm using:

public abstract class BaseClass { 
  public Guid Id { get; private set; }
  protected BaseClass(Guid id) { Id = id; } 
}     

public class DerivedClass : BaseClass 
{ 
  public DerivedClass(Guid id) : base(id) {} 
}

When I try to register the class for mongo serialization, I am getting an error:

var type = typeof(DerivedClass);
if (BsonClassMap.IsClassMapRegistered(type)) 
  return;
var cm = new BsonClassMap(type); cm.AutoMap();
BsonClassMap.RegisterClassMap(cm);

The error is:

The memberInfo argument must be for class DerivedClass, but was for class BaseClass.    Parameter name: memberInfo

Now, and this is where things start to get weird, when I tried to understand what was happening I made some changes to the BaseClass or the DerivedClass.

ANY of the two changes listed below will make the `RegisterClassMap` method work without errors...

change 1: adding a second, unused property on BaseClass

public abstract class BaseClass { 
  public Guid Id { get; private set; } 
  public string Test { get; }
  protected BaseClass(Guid id) { Id = id; } 
}

change 2: changing the Id property to have a non-private setter (any other works)

public abstract class BaseClass { 
  public Guid Id { get; protected set; }
  protected BaseClass(Guid id) { Id = id; } 
} 

THE QUESTION
My question is... what is happening? While I may agree that for the serializer you should have an accessible setter for every property on the class that you want to map (in this case, DerivedClass), why the case #1 is actually not giving any error?