Update graphqlMiddleware and parseBody

Author: danielrearden

src/index.js

@@ -255,7 +255,7 @@ export function graphqlHTTP(options: Options): Middleware {
 
       // Get GraphQL params from the request and POST body data.
       const { query, variables, operationName } = params;
-      showGraphiQL = canDisplayGraphiQL(request, params) && graphiql;
+      showGraphiQL = canDisplayGraphiQL(request, params) && graphiql !== false;
       if (typeof graphiql !== 'boolean') {
         graphiqlOptions = graphiql;
       }

src/parseBody.js

@@ -82,7 +82,8 @@ async function readBody(
   // TODO: Import the appropriate TS type and use it here instead
   typeInfo: {| type: string, parameters: { [param: string]: string, ... } |},
 ): Promise<string> {
-  const charset = (typeInfo.parameters.charset ?? 'utf-8').toLowerCase();
+  // flowlint-next-line unnecessary-optional-chain:off
+  const charset = typeInfo.parameters.charset?.toLowerCase() ?? 'utf-8';
 
   // Assert charset encoding per JSON RFC 7159 sec 8.1
   if (charset.slice(0, 4) !== 'utf-') {