address review comments

actix-http/src/body/message_body.rs

@@ -134,7 +134,7 @@ mod foreign_impls {
 
     impl<B> MessageBody for Box<B>
     where
-        B: MessageBody + Unpin,
+        B: MessageBody + Unpin + ?Sized,
     {
         type Error = B::Error;
 

actix-http/src/body/none.rs

@@ -40,4 +40,14 @@ impl MessageBody for None {
     ) -> Poll<Option<Result<Bytes, Self::Error>>> {
         Poll::Ready(Option::None)
     }
+
+    #[inline]
+    fn is_complete_body(&self) -> bool {
+        true
+    }
+
+    #[inline]
+    fn take_complete_body(&mut self) -> Bytes {
+        Bytes::new()
+    }
 }