fix(fetch): remove assertion on request.body.source on redirect (nodejs#2027) (nodejs#2028)

Fixes nodejs#2027

Author: macno

lib/fetch/index.js

@@ -1205,7 +1205,7 @@ async function httpRedirectFetch (fetchParams, response) {
   // 14. If request’s body is non-null, then set request’s body to the first return
   // value of safely extracting request’s body’s source.
   if (request.body != null) {
-    assert(request.body.source)
+    assert(request.body.source != null)
     request.body = safelyExtractBody(request.body.source)[0]
   }
 

test/fetch/redirect.js

@@ -27,3 +27,24 @@ test('Redirecting with a body does not cancel the current request - #1776', asyn
   t.equal(await resp.text(), '/redirect/')
   t.ok(resp.redirected)
 })
+
+test('Redirecting with an empty body does not throw an error - #2027', async (t) => {
+  const server = createServer((req, res) => {
+    if (req.url === '/redirect') {
+      res.statusCode = 307
+      res.setHeader('location', '/redirect/')
+      res.write('<a href="/redirect/">Moved Permanently</a>')
+      res.end()
+      return
+    }
+    res.write(req.url)
+    res.end()
+  }).listen(0)
+
+  t.teardown(server.close.bind(server))
+  await once(server, 'listening')
+
+  const resp = await fetch(`http://localhost:${server.address().port}/redirect`, { method: 'PUT', body: '' })
+  t.equal(await resp.text(), '/redirect/')
+  t.ok(resp.redirected)
+})