Check for empty content-type header.

.eslintrc.json

@@ -4,7 +4,7 @@
     "es2020": true,
     "node": true
   },
-  "extends": ["eslint:recommended", "plugin:react/recommended", "prettier", "next"],
+  "extends": ["eslint:recommended", "plugin:react/recommended", "prettier"],
   "parserOptions": {
     "ecmaFeatures": {
       "jsx": true

lib/request.js

@@ -88,7 +88,7 @@ export async function getClientInfo(req, { screen }) {
 }
 
 export function getJsonBody(req) {
-  if (req.headers['content-type'].indexOf('text/plain') !== -1) {
+  if ((req.headers['content-type'] || '').indexOf('text/plain') !== -1) {
     return JSON.parse(req.body);
   }