yarn start will throw error TypeError: Cannot read property "minimizer" of undefined

[jcppman]

Description

with the latest gatsby-plugin-netlify-cms package (https://github.com/gatsbyjs/gatsby/releases/tag/gatsby-plugin-netlify-cms%404.0.2), yarn start will throw error TypeError: Cannot read property "minimizer" of undefined.

This is caused by #14783. Because in dev mode optimization is indeed undefined.

Steps to reproduce

• clone the starter https://github.com/netlify-templates/gatsby-starter-netlify-cms/
• yarn
• update gatsby-plugin-netlify-cms to 4.0.2
• yarn start

Expected result

No error is thrown.

Actual result

An error will be thrown. TypeError: Cannot read property "minimizer" of undefined

Environment

System:
OS: macOS 10.14.5
CPU: (8) x64 Intel(R) Core(TM) i7-4980HQ CPU @ 2.80GHz
Shell: 2.6.0 - /usr/local/bin/fish
Binaries:
Node: 8.11.2 - ~/.config/fnm/bin/node
Yarn: 1.16.0 - /usr/local/bin/yarn
npm: 6.5.0 - ~/.config/fnm/bin/npm
Languages:
Python: 2.7.10 - /usr/bin/python
Browsers:
Chrome: 74.0.3729.169
Firefox: 64.0.2
Safari: 12.1.1
npmPackages:
gatsby: ^2.1.34 => 2.9.4
gatsby-image: ^2.0.23 => 2.1.4
gatsby-plugin-netlify: ^2.0.6 => 2.0.17
gatsby-plugin-netlify-cms: ^4.0.0 => 4.0.2
gatsby-plugin-purgecss: ^4.0.0 => 4.0.0
gatsby-plugin-react-helmet: ^3.0.4 => 3.0.12
gatsby-plugin-sass: ^2.0.7 => 2.0.11
gatsby-plugin-sharp: ^2.0.15 => 2.1.5
gatsby-remark-copy-linked-files: ^2.0.7 => 2.0.13
gatsby-remark-images: ^3.0.1 => 3.0.16
gatsby-remark-relative-images: ^0.2.1 => 0.2.2
gatsby-source-filesystem: ^2.0.26 => 2.0.39
gatsby-transformer-remark: ^2.3.4 => 2.4.0
gatsby-transformer-sharp: ^2.1.9 => 2.1.21

[sidharthachatterjee]

Fixed and published in gatsby-plugin-netlify-cms@4.0.3