Fix Headers bug in IE11

When calling `new Headers(undefined)` in IE11 an `Invalid argument` exception is thrown. With this in place, we'll call it with an empty object, resulting in an empty Headers object.
apollographql · Apr 25, 2019 · 78825c6 · 78825c6
1 parent d0ba386
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ### vNEXT
 
 - Allow `GraphQLRequestListener` callbacks in plugins to depend on `this`. [PR #2470](https://github.com/apollographql/apollo-server/pull/2470)
+- Fix `Invalid argument` in IE11, when using `apollo-datasource-rest` when `this.headers` is `undefined`. [PR #2607](https://github.com/apollographql/apollo-server/pull/2607)
 
 ### v2.4.8
 

diff --git a/packages/apollo-datasource-rest/src/RESTDataSource.ts b/packages/apollo-datasource-rest/src/RESTDataSource.ts
@@ -201,7 +201,7 @@ export abstract class RESTDataSource<TContext = any> extends DataSource {
     }
 
     if (!(init.headers && init.headers instanceof Headers)) {
-      init.headers = new Headers(init.headers);
+      init.headers = new Headers(init.headers || {});
     }
 
     const options = init as RequestOptions;