Do not use this. It was an early prototype. Since ASP.NET Core version 5.0, Blazor has a built-in <InputFile> component with more features and full support.
For details, see https://docs.microsoft.com/en-us/aspnet/core/blazor/file-uploads?view=aspnetcore-5.0
Everyone using the code from this repo should switch to using the framework's built-in implementation now.