// The following will map .NET Pascal Cased properties to bson Camel Cased properties.
            var conventionPack = new ConventionPack
            {
                new CamelCaseElementNameConvention(), new IgnoreExtraElementsConvention(true)
            };
            ConventionRegistry.Register("camelCase", conventionPack, t => true);
            
            clientSettings.ClusterConfigurator = cb =>
            {
                // This makes the output strictly JSON, such that we can format the logged commands.
                // The output can still be used in a shell (ex NoSqlBooster)
                // Without this, the output can contain JS code, such a regular expression literals
                // which would fail to format in a JSON formatter.
                var jsonWriterSettings = new JsonWriterSettings { OutputMode = JsonOutputMode.Strict };
                cb.Subscribe<CommandStartedEvent>(e =>
                {
                    if (_logger.IsEnabled(LogLevel.Debug))
                    {
                        _logger.LogDebug($"MongoDb - {e.CommandName} - {e.Command.ToJson(jsonWriterSettings)}");
                    }
                });
            };

// ...
.Project(augmentedProductType => new ProductTypeSearchResult
{
  Description = augmentedProductType.ExternalProductTypeDescription
})

 private const string ProjectionStage = @"
{
   "$project":{
      "Description":"$externalProductTypeDesc"
   }
}

 private static readonly PipelineStageDefinition<SearchAugmentedProductType, ProductTypeSearchResult>
            ProjectionPipelineStageDefinition = "theLoggedCommand";
.AppendStage(ProjectionPipelineStageDefinition);

 private const string ProjectionStage = @"
{
   "$project":{
      "description":"$externalProductTypeDesc"
   }
}