From 5248e182fef7c5d6e2ad166d6743d27ad5e20301 Mon Sep 17 00:00:00 2001
From: Fonger <5862369+Fonger@users.noreply.github.com>
Date: Wed, 15 Apr 2020 07:12:02 +0800
Subject: [PATCH] fix(export): fallback to empty string for basePath (#11880)

* fix(next-server): fallback to empty string for basePath

* Revert extra change and add unit test

Co-authored-by: JJ Kasper <jj@jjsweb.site>
---
 packages/next/next-server/lib/router/router.ts | 2 +-
 test/unit/router-add-base-path.test.js         | 9 +++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)
 create mode 100644 test/unit/router-add-base-path.test.js

diff --git a/packages/next/next-server/lib/router/router.ts b/packages/next/next-server/lib/router/router.ts
index b7084450359bd..6fc5be2fb0cdc 100644
--- a/packages/next/next-server/lib/router/router.ts
+++ b/packages/next/next-server/lib/router/router.ts
@@ -16,7 +16,7 @@ import { isDynamicRoute } from './utils/is-dynamic'
 import { getRouteMatcher } from './utils/route-matcher'
 import { getRouteRegex } from './utils/route-regex'
 
-const basePath = process.env.__NEXT_ROUTER_BASEPATH as string
+const basePath = (process.env.__NEXT_ROUTER_BASEPATH as string) || ''
 
 export function addBasePath(path: string): string {
   return path.indexOf(basePath) !== 0 ? basePath + path : path
diff --git a/test/unit/router-add-base-path.test.js b/test/unit/router-add-base-path.test.js
new file mode 100644
index 0000000000000..ab308dd20f578
--- /dev/null
+++ b/test/unit/router-add-base-path.test.js
@@ -0,0 +1,9 @@
+/* eslint-env jest */
+import { addBasePath } from 'next/dist/next-server/lib/router/router'
+
+describe('router addBasePath', () => {
+  it('should add basePath correctly when no basePath', () => {
+    const result = addBasePath('/hello')
+    expect(result).toBe('/hello')
+  })
+})