diff --git a/lib/streams.js b/lib/streams.js
index 5db2f13..5ac7e9a 100644
--- a/lib/streams.js
+++ b/lib/streams.js
@@ -237,8 +237,7 @@ function transform(input, process = () => undefined, finish = () => undefined, q
   }
   const result1 = process(input);
   const result2 = finish();
-  if (result1 !== undefined && result2 !== undefined) return concat([result1, result2]);
-  return result1 !== undefined ? result1 : result2;
+  return concat([result1, result2].filter(result => result !== undefined));
 }
 
 /**
@@ -263,8 +262,7 @@ async function transformAsync(
   }
   const result1 = await process(input);
   const result2 = await finish();
-  if (result1 !== undefined && result2 !== undefined) return concat([result1, result2]);
-  return result1 !== undefined ? result1 : result2;
+  return concat([result1, result2].filter(result => result !== undefined));
 }
 
 function _transformStream(input, process, finish, queuingStrategy) {