Prefer empty values from ValueFilter over request's header value in HeaderPropagation

src/Middleware/HeaderPropagation/src/HeaderPropagationMiddleware.cs

@@ -76,11 +76,7 @@ private static StringValues GetValue(HttpContext context, HeaderPropagationEntry
             context.Request.Headers.TryGetValue(entry.InboundHeaderName, out var value);
             if (entry.ValueFilter != null)
             {
-                var filtered = entry.ValueFilter(new HeaderPropagationContext(context, entry.InboundHeaderName, value));
-                if (!StringValues.IsNullOrEmpty(filtered))
-                {
-                    value = filtered;
-                }
+                value = entry.ValueFilter(new HeaderPropagationContext(context, entry.InboundHeaderName, value));
             }
 
             return value;

src/Middleware/HeaderPropagation/test/HeaderPropagationMiddlewareTest.cs

@@ -157,6 +157,20 @@ public async Task PreferValueFilter_OverRequestHeader()
             Assert.Equal("test", CapturedHeaders["in"]);
         }
 
+        [Fact]
+        public async Task PreferEmptyValuesFromValueFilter_OverRequestHeader()
+        {
+            // Arrange
+            Configuration.Headers.Add("in", (context) => StringValues.Empty);
+            Context.Request.Headers.Add("in", "no");
+
+            // Act
+            await Middleware.Invoke(Context);
+
+            // Assert
+            Assert.DoesNotContain("in", CapturedHeaders.Keys);
+        }
+
         [Fact]
         public async Task EmptyValuesFromValueFilter_DoesNotAddIt()
         {