npm "Cannot read properties of null" Engine Error in CI - Fix Corrupted State

By Kaveh Alemi·Latchkey

A "Cannot read properties of null" crash from the npm engine is an internal error, usually triggered by a malformed lockfile, a corrupted cache, or an npm version that mishandles your tree.

What this error means

npm install or npm ci throws a TypeError that it cannot read a property (often reading or matches) of null, with a stack trace inside npm internals rather than your code.

npm ERR! Cannot read properties of null (reading 'matches')
npm ERR! A complete log of this run can be found in:
npm ERR! /home/runner/.npm/_logs/2026-06-26T00_00_00_000Z-debug.log

Common causes

A corrupted lockfile or cache

A malformed package-lock.json or a poisoned ~/.npm cache feeds null into npm internals, crashing the resolver.

An npm version mismatch with the lockfile format

An old npm reading a newer lockfileVersion (or the reverse) can hit code paths that assume data that is not present.

How to fix it

Clear state and reinstall clean

1. Remove node_modules, package-lock.json, and clean the cache.
2. Reinstall so npm rebuilds a consistent tree.

rm -rf node_modules package-lock.json
npm cache clean --force
npm install

Align the npm version

1. Pin a known-good npm version in CI.
2. Regenerate the lockfile with that version and commit it.

npm install -g npm@10

How to prevent it

• Pin one npm version across local and CI, commit a lockfile generated by it, and cache ~/.npm keyed on the lockfile so corruption does not persist across runs.

Frequently asked questions

Related guides

References

• Node.js documentation
• npm CLI documentation
• GitHub Actions documentation