diff --git a/package.json b/package.json
index b7db4e4..4ee52dd 100644
--- a/package.json
+++ b/package.json
@@ -4,8 +4,8 @@
   "author": "Jörn-Michael Miehe <joern-michael.miehe@lenaisten.de>",
   "license": "MIT",
   "scripts": {
-    "build": "webpack --mode=development",
-    "build-release": "webpack --mode=production",
+    "build-debug": "webpack --mode=development",
+    "build": "webpack --mode=production",
     "lint-ext": "web-ext lint --source-dir=dist",
     "build-ext": "web-ext build --source-dir=dist --artifacts-dir=dist --overwrite-dest"
   },
diff --git a/src/bttv_api.ts b/src/bttv_api.ts
index 0ee9133..415eb32 100644
--- a/src/bttv_api.ts
+++ b/src/bttv_api.ts
@@ -13,12 +13,9 @@ type BTTV_Emote = {
  * Query BTTV API for an emote graphic
  *
  * @param code string associated with the emote graphic (often called "emote" itself)
- * @returns `null` iff no emote found or error,
- * else `[code, url]` tuple where `url` is the URL to a BTTV emote graphic
+ * @returns `null` iff no emote found or error, else URL to a BTTV emote graphic
  */
-export async function bttv_get_url(
-  code: string,
-): Promise<[string, string] | null> {
+export async function bttv_get_url(code: string): Promise<string | null> {
   // search for emotes
   const res = await fetch(
     `https://api.betterttv.net/3/emotes/shared/search?query=${code}&offset=0&limit=50`,
@@ -37,8 +34,5 @@ export async function bttv_get_url(
   if (matches.length <= 0) return null;
 
   // return first emote's URL
-  return [
-    code,
-    `//cdn.betterttv.net/emote/${matches[0].id}/1x.${matches[0].imageType}`,
-  ];
+  return `//cdn.betterttv.net/emote/${matches[0].id}/1x.${matches[0].imageType}`;
 }
diff --git a/src/helpers.ts b/src/helpers.ts
index 7c8203b..af652cf 100644
--- a/src/helpers.ts
+++ b/src/helpers.ts
@@ -1,8 +1,3 @@
-/**
- * Async function mapping some `input` to an `[input, output]` tuple or a `null` if no output exists
- */
-type MapFunction<In, Out> = (input: In) => Promise<[In, Out] | null>;
-
 /**
  * Concurrently create some mapping of input to output elements.
  *
@@ -12,13 +7,13 @@ type MapFunction<In, Out> = (input: In) => Promise<[In, Out] | null>;
  */
 export async function map_concurrent<In, Out>(
   inputs: Iterable<In>,
-  map_fn: MapFunction<In, Out>,
-): Promise<Map<In, Out>> {
+  map_fn: (input: In) => Promise<Out | null>,
+): Promise<Map<In, Out | null>> {
   // apply map_fn to inputs
-  const queue = [...inputs].map((input) => map_fn(input));
+  const outputs = await Promise.all([...inputs].map((input) => map_fn(input)));
 
-  // wait for calls to finish
-  return new Map<In, Out>(
-    (await Promise.all(queue)).filter((job): job is [In, Out] => job !== null),
+  // create map object
+  return new Map<In, Out | null>(
+    [...inputs].map((input, index) => [input, outputs[index]]),
   );
 }
diff --git a/src/main.ts b/src/main.ts
index 7d68f95..4583853 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -24,13 +24,13 @@ async function process_text(text: string): Promise<string> {
   for (const emote of matches.reverse()) {
     const [match, code] = emote;
 
-    if (!emotes.has(code)) continue;
-    // emote exists
+    // ensure emote exists
     const url = emotes.get(code);
+    if (url == null) continue;
 
-    if (emote.index == undefined) continue;
-    // position in input string is known
+    // ensure position in input string is known
     const index = emote.index;
+    if (index == undefined) continue;
 
     text =
       text.substring(0, index) +