Get RangeError when used with multiple mounts

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# Error Reported

RangeError: Maximum call stack size exceeded
at RegExp.test (native)
at ServerResponse.res.render [as _render]
## Happens when I use multiple mounts.
### e.g

var app = express()
...
app.use(helper('appName))
app.use(appRouter)
### mount 1

server.use(app)

var admin = express()

//same name or different name does not matter
admin.use(helper('appName'))

//all routes fails in 'res.render()' call with above error
app.use(adminRouter)
### mount 2

server.use(admin)

Start by reproducing the RangeError with the two mounted Express apps shown in the issue, using helper('appName') and a route that calls res.render. Trace the helper and render path while comparing the app and admin mounts. Done means the multiple-mount example renders without exceeding the call stack.

Written by the indexing model from the issue text.