diff --git a/README.md b/README.md
index d269b1d..3845d30 100644
--- a/README.md
+++ b/README.md
@@ -19,7 +19,6 @@ A public GraphQL API for information about countries, continents, and languages.
 3. Each `Country` has an array of `states` populated by their states/provinces, if any.
 
 - [Writing queries](#writing-queries)
-  - [Migration notes (pre-March 2020)](#migration-notes-pre-march-2020)
 - [Docs](#docs)
 - [Examples](#examples)
 - [License](#license)
@@ -28,7 +27,7 @@ A public GraphQL API for information about countries, continents, and languages.
 
 ```graphql
 {
-  country(code: BR) {
+  country(code: "BR") {
     name
     native
     capital
@@ -64,20 +63,6 @@ The above GraphQL query will produce the following JSON response:
 }
 ```
 
-### Migration notes (pre-March 2020)
-
-In the first version of this API, `code` arguments were treated as `String`s. Now, they are enums of valid options only. To migrate, simply remove the double quotes from your existing code arguments:
-
-```diff
-{
-- country(code: "CA") {
-+ country(code: CA) {
-    name
-    emoji
-  }
-}
-```
-
 ## Docs
 
 Check out [the playground](https://countries.trevorblades.com) to explore the schema and test out some queries.
diff --git a/index.js b/index.js
index 148fa6a..5804872 100644
--- a/index.js
+++ b/index.js
@@ -3,26 +3,14 @@ const {ApolloServer, gql} = require('apollo-server');
 const {continents, countries, languages} = require('countries-list');
 
 const typeDefs = gql`
-  enum ContinentCode {
-    ${Object.keys(continents)}
-  }
-
-  enum CountryCode {
-    ${Object.keys(countries)}
-  }
-
-  enum LanguageCode {
-    ${Object.keys(languages)}
-  }
-
   type Continent {
-    code: ContinentCode!
+    code: ID!
     name: String!
     countries: [Country!]!
   }
 
   type Country {
-    code: CountryCode!
+    code: ID!
     name: String!
     native: String!
     phone: String!
@@ -42,7 +30,7 @@ const typeDefs = gql`
   }
 
   type Language {
-    code: LanguageCode!
+    code: ID!
     name: String
     native: String
     rtl: Boolean!
@@ -50,11 +38,11 @@ const typeDefs = gql`
 
   type Query {
     continents: [Continent!]!
-    continent(code: ContinentCode!): Continent!
+    continent(code: ID!): Continent
     countries: [Country!]!
-    country(code: CountryCode!): Country!
+    country(code: ID!): Country
     languages: [Language!]!
-    language(code: LanguageCode!): Language!
+    language(code: ID!): Language
   }
 `;
 
@@ -104,10 +92,13 @@ const resolvers = {
   },
   Query: {
     continent(parent, {code}) {
-      return {
-        code,
-        name: continents[code]
-      };
+      const name = continents[code];
+      return (
+        name && {
+          code,
+          name
+        }
+      );
     },
     continents() {
       return Object.entries(continents).map(([code, name]) => ({
@@ -117,10 +108,12 @@ const resolvers = {
     },
     country(parent, {code}) {
       const country = countries[code];
-      return {
-        ...country,
-        code
-      };
+      return (
+        country && {
+          ...country,
+          code
+        }
+      );
     },
     countries() {
       return Object.entries(countries).map(([code, country]) => ({
@@ -130,10 +123,12 @@ const resolvers = {
     },
     language(parent, {code}) {
       const language = languages[code];
-      return {
-        ...language,
-        code
-      };
+      return (
+        language && {
+          ...language,
+          code
+        }
+      );
     },
     languages() {
       return Object.entries(languages).map(([code, language]) => ({