Looking at the source code for BsonArray.cs, there are numerous places where null values in the array will cause a crash.

line 676:
clone.Add(value.DeepClone());

line 722:
hash = 37 * hash + value.GetHashCode();

line 818:
sb.Append(_values[i].ToString());

line 833:
_values[i].WriteTo(bsonWriter);

..and I'm sure there are other places!

To reproduce: deserialize some JSON with a null in an array, then try adding to Mongo with the driver.

My understanding is that null values are valid JSON and valid BSON, so should be supported by Mongo and the C# driver.

I'm happy to work on this - but am too busy this week.

Thanks,
Ben