DownloadIndexableLoadFieldsProcessor.cs

public abstract class DownloadIndexableLoadFieldsProcessor
{
    public virtual void Process(DownloadEventIndexableLoadFieldsPipelineArgs args)
    {
        if (args == null)
            throw new ArgumentNullException(nameof(args));
        args.Fields.AddRange(this.GetFields(args));
    }

    protected abstract IEnumerable<IIndexableDataField> GetFields(DownloadEventIndexableLoadFieldsPipelineArgs args);
}