Reset SSE event type after an empty event block

src/libraries/System.Net.ServerSentEvents/src/System/Net/ServerSentEvents/SseParser_1.cs

@@ -265,6 +265,7 @@ private bool ProcessLine(out SseItem<T> sseItem)
                     return true;
                 }
 
+                _eventType = null;
                 _lineBuffer.Discard(advance);
                 sseItem = default;
                 return false;

src/libraries/System.Net.ServerSentEvents/tests/SseParserTests.cs

@@ -168,6 +168,25 @@ await ReadAllEventsAsync(stream) :
             AssertSseItemEqual(new SseItem<string>("This is the third message.", "message"), items[2]);
         }
 
+        [Theory]
+        [MemberData(nameof(NewlineTrickleAsyncData))]
+        public async Task Parse_EventWithoutData_ResetsEventType(string newline, bool trickle, bool useAsync)
+        {
+            using Stream stream = GetStream(
+                $"event: stale{newline}id: 2{newline}retry: 300{newline}{newline}" +
+                $"data: first{newline}data: second{newline}{newline}" +
+                $"event: stale{newline}{newline}data: third{newline}{newline}", trickle);
+
+            List<SseItem<string>> items = useAsync ?
+                await ReadAllEventsAsync(stream) :
+                ReadAllEvents(stream);
+
+            Assert.Equal(2, items.Count);
+            AssertSseItemEqual(new SseItem<string>("first\nsecond", "message")
+                { EventId = "2", ReconnectionInterval = TimeSpan.FromMilliseconds(300) }, items[0]);
+            AssertSseItemEqual(new SseItem<string>("third", "message"), items[1]);
+        }
+
         [Theory]
         [MemberData(nameof(NewlineTrickleAsyncData))]
         public async Task Parse_HtmlSpec_Example2(string newline, bool trickle, bool useAsync)