[TestMethod]
public void ShouldRaiseBetterErrors()
{
    const string CONN = "mongodb://localhost:27017";
    var client = new MongoClient(MongoUrl.Create(CONN));
    var database = client.GetDatabase("test");
    database.DropCollection("foo");
    var collection = database.GetCollection<BsonDocument>("foo");

    var search = "Test\0Test";
    var regex = new BsonRegularExpression(string.Format(".*{0}.*", search), "i");
    var filter = Builders<BsonDocument>.Filter.Gt("_id", regex);
    try
    {
        var result = collection.Find(filter).FirstOrDefault();
    }
    catch (ArgumentException e) when (e.Message == "A CString cannot contain null bytes." && e.ParamName == "value")
    {
        throw new ApplicationException("You are trying to query with a string that contains a null character, this is not supported");
    }
}

public enum ErrorCodes
{
  //...
  InvalidCString = 10001
  //...
}
// ...
namespace MongoDB.Bson.IO
{
    internal static class CStringUtf8Encoding
    {
        public static int GetBytes(string value, byte[] bytes, int byteIndex, UTF8Encoding fallbackEncoding)
        {
            var charLength = value.Length;
            var initialByteIndex = byteIndex;

            for (var charIndex = 0; charIndex < charLength; charIndex++)
            {
                var c = (int)value[charIndex];
                if (c == 0)
                {
                    throw new MongoDriverException { Code = ErrorCodes.InvalidCString, Message = "A CString cannot contain null bytes.", ... });
                }
                // ...
            }
            // ...
        }
    }
}