Improved the code with some minor changes

src/stream/stream/merge.rs

@@ -62,12 +62,11 @@ where
     S: Stream<Item = I>,
 {
     match first.poll_next(cx) {
-        Poll::Ready(Some(item)) => Poll::Ready(Some(item)),
         Poll::Ready(None) => second.poll_next(cx),
+        Poll::Ready(item) => Poll::Ready(item),
         Poll::Pending => match second.poll_next(cx) {
-            Poll::Ready(Some(item)) => Poll::Ready(Some(item)),
-            Poll::Ready(None) => Poll::Pending,
-            Poll::Pending => Poll::Pending,
+            Poll::Ready(None) | Poll::Pending => Poll::Pending,
+            Poll::Ready(item) => Poll::Ready(item),
         },
     }
 }

src/stream/stream/mod.rs

@@ -1663,18 +1663,14 @@ extension_trait! {
             ```
             # async_std::task::block_on(async {
             use async_std::prelude::*;
-            use async_std::stream;
+            use async_std::stream::{self, FromStream};
 
             let a = stream::once(1u8);
             let b = stream::once(2u8);
             let c = stream::once(3u8);
 
-            let mut s = a.merge(b).merge(c);
-            let mut lst = Vec::new();
-
-            while let Some(n) = s.next().await {
-                lst.push(n)
-            }
+            let s = a.merge(b).merge(c);
+            let mut lst = Vec::from_stream(s).await;
 
             lst.sort_unstable();
             assert_eq!(&lst, &[1u8, 2u8, 3u8]);