ParseStyleSheetAsync throws NPE on empty string

[Fraaankes]

Bug Report

Prerequisites

• Can you reproduce the problem in a MWE?
• Are you running the latest version of AngleSharp?
• Did you check the FAQs to see if that helps you?
• Are you reporting to the correct repository? (there are multiple AngleSharp libraries, e.g., AngleSharp.Css for CSS support)
• Did you perform a search in the issues?

For more information, see the CONTRIBUTING guide.

Description

Calling CssParser.ParseStyleSheetAsync("") throws a System.NullReferenceException.

Steps to Reproduce

Code:

class Program
    {
        static async Task Main(string[] args)
        {
            var parser = new CssParser();
            var s = await parser.ParseStyleSheetAsync("");

            Console.WriteLine(s);
        }
    }

Stacktrace:
Unhandled exception. System.NullReferenceException: Object reference not set to an instance of an object.
at AngleSharp.Text.TextSource.DetectByteOrderMarkAsync(CancellationToken cancellationToken)
at AngleSharp.Text.TextSource.PrefetchAllAsync(CancellationToken cancellationToken)
at AngleSharp.Css.Parser.CssParser.ParseStyleSheetAsync(String content, CancellationToken cancelToken)

Expected behavior: [What you expected to happen]
To behave like the non-async version which correctly parses the empty string and returns an empty stylesheet.

Environment details: [OS, .NET Runtime, ...]
Windows 10
.NET Core 3.0.100

[FlorianRappl]

Thanks for the report. I'll look into it!

[FlorianRappl]

Landed in devel and the preview on NuGet.