Deserializing field when type is changed using MongoDb csharp driver

I am testing a number of scenarios with MongoDb to see how to recover from possible data issues.

I have classes (Addresses with collection of Address) with a zipcode property in Address which was originally cast as string. I saved out multiple records of Addresses and could retrieve them all fine. like this, var allAddresses = addresses.FindAllAs();

I changed the zip code property to int and saved some records. I then changed the zip code property back to string.

When I attempt to read the collection back I get an error deserializing, as expected. var allAddresses = addresses.FindAllAs();

My goal is to be able to override the deserialization so if an field deserialization error occurs I can choose to either ignore it or apply a default value.

I have tried a custom serializer, which is not working. Any suggestions would be appreciated.

public class MyCustomSerializer : BsonBaseSerializer
  {

    public override object Deserialize(BsonReader bsonReader, Type nominalType,  IBsonSerializationOptions options)
    {
      if (bsonReader.CurrentBsonType != BsonType.String)
      {
        return string.Empty;
      }

      return bsonReader.ReadString();
    }

    public override void Serialize(
               BsonWriter bsonWriter,
               Type nominalType,
               object value,
               IBsonSerializationOptions options)
    {
      bsonWriter.WriteStartDocument();
      bsonWriter.WriteName("ZipCode");
      bsonWriter.WriteString(value.ToString());
      bsonWriter.WriteEndDocument();
    }
  }