[NPM ERR!] Could not find file: config/.json

After npm install and then running npm run dev, my cli shows an npm ERR!:

Could not find file: config/.json
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! atag-report-tool@0.6.0 replace_vars: `mustache config/$NODE_ENV.json src/index.html > public/index.html`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the atag-report-tool@0.6.0 replace_vars script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

Other specifics:

• ATAG-report-tool at commit d97d450
• MacOs 10.15.3
• node 12.18.3 (--lts), 13.8.0

[dmundra]

I got the same error and from the readme I found the step that is needed:

Before running npm run build or npm run dev, set export NODE_ENV=[environment-name]