[apollo-server-plugin-base] fix GraphQLRequestListener type def… (#2368)

* fix GraphQLRequestListener type definitions

* update changelog

* Adjust CHANGELOG.md for #2368.

CHANGELOG.md

@@ -6,6 +6,8 @@ The version headers in this history reflect the versions of Apollo Server itself
 
 > The changes noted within this `vNEXT` section have not been released yet. New PRs and commits which introduce changes should include an entry in this `vNEXT` section as part of their development. When a release is being prepared, a new header will be (manually) created below and the the appropriate changes within that release will be moved into the new section.
 
+- `apollo-server-plugin-base`: Fix `GraphQLRequestListener` type definitions to allow `return void`. [PR #2368](https://github.com/apollographql/apollo-server/pull/2368)
+
 ### v2.6.7
 
 > [See complete versioning details.](https://github.com/apollographql/apollo-server/commit/183de5f112324def375a45c239955e1bf1608fae)

packages/apollo-server-plugin-base/src/index.ts

@@ -29,13 +29,13 @@ export interface GraphQLRequestListener<TContext = Record<string, any>> {
  GraphQLRequestContext<TContext>,
  'metrics' | 'source'
  >,
- ): (err?: Error) => void | void;
+ ): ((err?: Error) => void) | void;
  validationDidStart?(
  requestContext: WithRequired<
  GraphQLRequestContext<TContext>,
  'metrics' | 'source' | 'document'
  >,
- ): (err?: ReadonlyArray<Error>) => void | void;
+ ): ((err?: ReadonlyArray<Error>) => void) | void;
  didResolveOperation?(
  requestContext: WithRequired<
  GraphQLRequestContext<TContext>,
@@ -64,7 +64,7 @@ export interface GraphQLRequestListener<TContext = Record<string, any>> {
  GraphQLRequestContext<TContext>,
  'metrics' | 'source' | 'document' | 'operationName' | 'operation'
  >,
- ): (err?: Error) => void | void;
+ ): ((err?: Error) => void) | void;
  willSendResponse?(
  requestContext: WithRequired<
  GraphQLRequestContext<TContext>,