Build suddenly fails ( bash: yarn: command not found )

I need advice to debug deploy https://app.netlify.com/sites/pedantic-ramanujan-154879/deploys/5ed950b2f293b5000819f835

I have to admit that I’ve no idea why it isn’t building since I can build it “on my machine”. Anyone who can see what is causing this?

9:52:11 PM: $ yarn build
9:52:11 PM: bash: yarn: command not found
9:52:11 PM: ​
9:52:11 PM: ┌─────────────────────────────┐
9:52:11 PM: │   "build.command" failed    │
9:52:11 PM: └─────────────────────────────┘
9:52:11 PM: ​
9:52:11 PM:   Error message
9:52:11 PM:   Command failed with exit code 127: yarn build
9:52:11 PM: ​
9:52:11 PM:   Error location
9:52:11 PM:   In Build command from settings:
9:52:11 PM:   yarn build
9:52:11 PM: ​
9:52:11 PM:   Resolved config
9:52:11 PM:   build:
9:52:11 PM:     command: yarn build
9:52:11 PM:     publish: /opt/build/repo/build

SOLUTION
So the solution to this issue was quite simple, all I had to do was to install netlify-cli as a devDependencie.