Summary

BsonClassMapSerializer throws a NullReferenceException when BsonClassMap::CreateInstance() returns null, which may happen if one has configured a creator on the map and that creator fails silently returning nulls instead of object instances (think of DI containers)

How to Reproduce

Simulate a failing creator:

BsonClassMap .LookupClassMap(typeof(MyModel)) .SetCreator(() => {
//could be something like:
        //ServiceProvider.GetService(domainObjType)

        //that may...
        return null;
}); 

Execute a Find() on that type:

var filter = SetupTheFilterDefinition();
var results = collection.Find<MyModel>(filter).ToList();