Update

Author: JunTaoLuo

src/Microsoft.AspNetCore.Http.Abstractions/Internal/ParsingHelpers.cs

@@ -26,7 +26,7 @@ private static IEnumerable<string> GetHeaderSplitImplementation(StringValues val
         {
             foreach (var segment in new HeaderSegmentCollection(values))
             {
-                if (segment.Data.HasValue && !string.IsNullOrWhiteSpace(segment.Data.Value))
+                if (segment.Data.HasValue && !StringSegment.IsNullOrEmpty(segment.Data))
                 {
                     yield return DeQuote(segment.Data.Value);
                 }

test/Microsoft.AspNetCore.Http.Tests/HeaderDictionaryTests.cs

@@ -16,9 +16,9 @@ public class HeaderDictionaryTests
           new[] { "Value1", "Value2", "Value3", "Value4" },
           new[] { "Value1", "", "Value3", "Value4" },
           new[] { "Value1", "", "", "Value4" },
-          new[] { "Value1", "", " ", "Value4" },
+          new[] { "Value1", "", null, "Value4" },
           new[] { "", "", "", "" },
-          new[] { "", " ", "", " " }
+          new[] { "", null, "", null },
         };
 
         [Fact]