What causes "CommonJS's exports must not be null" in grafana/k6?

Replace 'module.exports = null' with 'module.exports = {}' in the offending file

CommonJS's exports must not be null

Error message

CommonJS's exports must not be null

What it means

After executing a CommonJS module's factory function, k6 reads back the module's 'exports' property; if the script assigned module.exports = null, k6 refuses to load it because there is no object to import from. This check lives in the cjsmodule loader and fires during require()/import resolution, before the test runs.

Source

Thrown at js/modules/cjsmodule.go:83

	if err != nil {
		return nil, err
	}

	module := rt.NewObject()
	cmi.exports = rt.NewObject()
	_ = module.Set("exports", cmi.exports)
	call, ok := sobek.AssertFunction(v)
	if !ok {
		panic("Somehow a CommonJS module is not wrapped in a function - " +
			"this is a k6 bug, please report it (https://github.com/grafana/k6/issues)")
	}
	if _, err = call(cmi.exports, module, cmi.exports); err != nil {
		return nil, err
	}

	exportsV := module.Get("exports")
	if sobek.IsNull(exportsV) {
		return nil, errors.New("CommonJS's exports must not be null")
	}
	cmi.exports = exportsV.ToObject(rt)

	// this will be called multiple times we only need to update this on the first VU
	if cmi.w.exportedNames == nil {
		cmi.w.exportedNames = cmi.exports.Keys()
		if cmi.w.exportedNames == nil { // workaround if a CommonJS module does not have exports
			cmi.w.exportedNames = make([]string, 0)
		}
		for _, callback := range cmi.w.exportedNamesCallbacks {
			callback(cmi.w.exportedNames)
		}
	}
	__esModule := cmi.exports.Get("__esModule") //nolint:revive
	cmi.isEsModuleMarked = __esModule != nil && __esModule.ToBoolean()
	return cmi, nil
}

View on GitHub (pinned to 93accf6570)

Solutions

Replace 'module.exports = null' with 'module.exports = {}' in the offending file
If the assignment is conditional, export an empty object in the else branch instead of null
For third-party code, vendor/patch it or import a different entry point that does not null its exports

Example fix

// before
module.exports = hasFeature ? featureApi : null;

// after
module.exports = hasFeature ? featureApi : {};

Defensive patterns

Strategy: validation

Validate before calling

// scan required files before running k6
grep -rn 'module.exports *= *null' src/ && { echo 'null exports found'; exit 1; }

Try / catch

Wrap the require in a script-level check only if conditional: use a shim file that re-exports an object (module.exports = dep ?? {}) so the loaded module never presents null exports.

Prevention

Never assign null to module.exports; use {}
Add an ESLint rule / grep in CI for 'module.exports = null'
After adding bundlers, smoke-test that every bundled module still imports

When it happens

Trigger: A required/imported .js file contains 'module.exports = null' (directly, through a re-export chain, or via a bundler/transpiler that emits it). The error names the loader, and the failing file appears in the require chain.

Common situations: Conditional exports at the end of a library ('module.exports = featureEnabled ? lib : null'); Babel/tsc output for modules with no exports; hand-written stub files that use null as 'nothing to export'.

Related errors

AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/05d09657337a849d. Report an issue: GitHub.