Calling reply without a payload on a JSONP route throws an error

[kschat]

This only occurs if the query parameter containing the JSONP function name is given. Code to reproduce:

'use strict';

const hapi = require('hapi');
const server = new hapi.Server();

server.connection({ port: 4000 });

server.route({
  method: 'GET',
  path: '/test',
  config: {
    jsonp: 'callback',
    handler(request, reply) {
      return reply();
    }
  }
});

server.start(() => console.log('server started'));

Requesting /test works fine, but requesting /test?callback=cb throws the following error:

Debug: internal, implementation, error
    TypeError: Cannot read property 'replace' of null
    at internals.Response._prepare.internals.Response._processPrepare.internals.Response._marshal.internals.Payload.jsonp (/home/kyle/Workspace/hapi-bug/node_modules/hapi/lib/response.js:625:71)
    at /home/kyle/Workspace/hapi-bug/node_modules/hapi/lib/transmit.js:135:35
    at internals.Response._prepare.internals.Response._processPrepare.internals.Response._marshal.internals.Response._streamify (/home/kyle/Workspace/hapi-bug/node_modules/hapi/lib/response.js:529:12)
    at internals.Response._prepare.internals.Response._processPrepare.internals.Response._marshal.next [as _marshal] (/home/kyle/Workspace/hapi-bug/node_modules/hapi/lib/response.js:470:21)
    at /home/kyle/Workspace/hapi-bug/node_modules/hapi/lib/transmit.js:124:18
    at /home/kyle/Workspace/hapi-bug/node_modules/hapi/lib/transmit.js:509:20
    at Object.exports.parallel (/home/kyle/Workspace/hapi-bug/node_modules/hapi/node_modules/items/lib/index.js:47:9)
    at Object.exports.send.internals.marshal.internals.fail.internals.transmit.internals.state.Items.parallel [as state] (/home/kyle/Workspace/hapi-bug/node_modules/hapi/lib/transmit.js:502:11)
    at Object.exports.send.internals.marshal.internals.state [as marshal] (/home/kyle/Workspace/hapi-bug/node_modules/hapi/lib/transmit.js:98:15)
    at Object.exports.send.callback [as send] (/home/kyle/Workspace/hapi-bug/node_modules/hapi/lib/transmit.js:30:15)

I've been able to reproduce on 13.0.0 and 13.4.0, but haven't tested on any other versions.

[hueniverse]

Can you PR a failing test?

[kschat]

Sure, I'll try to get that in today.

[kschat]

Looks like @nrotta beat me to the punch. If there's anything else I can do, please let me know.