Uncaught "missing resources" error on 404 page

[chenders]

Description

When running gatsby develop with gatsby@2.0.66, navigating to a URL that doesn't exist (as suggested in part seven of the tutorial) results in a nice 404 page like this:

Starting with gatsby@2.0.67, it results in an uncaught error:

Looking through the comparison between the two versions, it looks like #10224 might be the culprit.

Steps to reproduce

1. Create a new gatsby project from the hello world starter:

$  gatsby new testing-404 https://github.com/gatsbyjs/gatsby-starter-hello-world

2. Install gatsby@2.0.66, run gatsby develop and see the proper 404 page

$ cd testing-404
$ yarn add gatsby@2.0.66
$ gatsby develop
# visit http://localhost:8000/sdf

3. Stop gatsby-develop, install gatsby@2.0.67, run gatsby develop and note the uncaught error page

$ yarn add gatsby@2.0.67
$ gatsby develop
# visit http://localhost:8000/sdf

Expected result

404 page is displayed

Actual result

Uncaught error is displayed

Environment

 $ gatsby info --clipboard

  System:
    OS: macOS 10.14.2
    CPU: (8) x64 Intel(R) Core(TM) i7-7820HQ CPU @ 2.90GHz
    Shell: 3.2.57 - /bin/bash
  Binaries:
    Node: 11.3.0 - /usr/local/bin/node
    Yarn: 1.12.3 - /usr/local/bin/yarn
    npm: 6.4.1 - /usr/local/bin/npm
  Browsers:
    Chrome: 71.0.3578.98
    Firefox: 63.0.3
    Safari: 12.0.2
  npmPackages:
    gatsby: 2.0.67 => 2.0.67 
  npmGlobalPackages:
    gatsby-cli: 2.4.6