Fixed the null reference in empty content #42

Author: FlorianRappl

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 Released on Tuesday, March 31 2020.
 
+- Fixed issue with empty content (#42)
 - Fixed handling of CSS gradients (#45)
 - Improved CSS string representation of gradients (#46)
 - Added support for the .NET Framework 4.6.1 target

src/AngleSharp.Css.Tests/Parsing/StyleSheet.cs

@@ -0,0 +1,19 @@
+namespace AngleSharp.Css.Tests.Parsing
+{
+    using AngleSharp.Css.Parser;
+    using NUnit.Framework;
+    using System.Threading.Tasks;
+
+    [TestFixture]
+    public class StyleSheet
+    {
+        [Test]
+        public async Task ParseEmptySheet_Issue42()
+        {
+            var sheetCode = "";
+            var parser = new CssParser();
+            var sheet = await parser.ParseStyleSheetAsync(sheetCode);
+            Assert.IsNotNull(sheet);
+        }
+    }
+}

src/AngleSharp.Css/Parser/CssParser.cs

@@ -132,7 +132,12 @@ public ICssStyleSheet ParseStyleSheet(Stream content)
         public async Task<ICssStyleSheet> ParseStyleSheetAsync(String content, CancellationToken cancelToken)
         {
             var source = new TextSource(content);
-            await source.PrefetchAllAsync(cancelToken).ConfigureAwait(false);
+
+            if (content.Length > 0)
+            {
+                await source.PrefetchAllAsync(cancelToken).ConfigureAwait(false);
+            }
+
             return ParseStylesheet(source);
         }
 

src/AngleSharp.Css/Parser/CssParserExtensions.cs

@@ -17,31 +17,22 @@ public static class CssParserExtensions
         /// <param name="parser">The parser to extend.</param>
         /// <param name="content">The string content to parse.</param>
         /// <returns>The task yielding the created stylesheet.</returns>
-        public static Task<ICssStyleSheet> ParseStyleSheetAsync(this ICssParser parser, String content)
-        {
-            return parser.ParseStyleSheetAsync(content, CancellationToken.None);
-        }
+        public static Task<ICssStyleSheet> ParseStyleSheetAsync(this ICssParser parser, String content) => parser.ParseStyleSheetAsync(content, CancellationToken.None);
 
         /// <summary>
         /// Parses a CSS stylesheet from a string asynchronously.
         /// </summary>
         /// <param name="parser">The parser to extend.</param>
         /// <param name="content">The stream content to parse asynchronously.</param>
         /// <returns>The task yielding the created stylesheet.</returns>
-        public static Task<ICssStyleSheet> ParseStyleSheetAsync(this ICssParser parser, Stream content)
-        {
-            return parser.ParseStyleSheetAsync(content, CancellationToken.None);
-        }
+        public static Task<ICssStyleSheet> ParseStyleSheetAsync(this ICssParser parser, Stream content) => parser.ParseStyleSheetAsync(content, CancellationToken.None);
 
         /// <summary>
         /// Parses a CSS stylesheet from hosting stylesheet asynchronously.
         /// </summary>
         /// <param name="parser">The parser to extend.</param>
         /// <param name="sheet">The stylesheet containg the URL reference.</param>
         /// <returns>The task yielding the finished stylesheet.</returns>
-        public static Task<ICssStyleSheet> ParseStyleSheetAsync(this ICssParser parser, ICssStyleSheet sheet)
-        {
-            return parser.ParseStyleSheetAsync(sheet, CancellationToken.None);
-        }
+        public static Task<ICssStyleSheet> ParseStyleSheetAsync(this ICssParser parser, ICssStyleSheet sheet) => parser.ParseStyleSheetAsync(sheet, CancellationToken.None);
     }
 }