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JavaScript has two bottom values — null and undefined — which creates unnecessary complexity. Using undefined exclusively keeps the language model simpler: uninitialized variables, missing object properties, and absent function arguments are all naturally undefined. This rule disallows the null literal and encourages undefined as the single bottom value.
Recommended✅ recommended
Fixable🔧 Auto-fixable
Suggestions💡 Has suggestions
// Assigning null to a variable
let foo = null;

// Loose equality check against null
if (bar == null) {}

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Autofix and suggestions

The rule’s fix behavior depends on context:
  • Loose equality (== null, != null) — automatically replaced with undefined.
  • return null — suggests either removing null (making the return implicit) or replacing it with undefined.
  • let foo = null — suggests either removing the initializer entirely or replacing it with undefined.
  • All other cases — suggests replacing null with undefined.

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Configuration options

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checkStrictEquality

Type: boolean
Default: false By default, strict equality checks (=== null, !== null) are ignored, since they are a common and intentional pattern for detecting null specifically. Set to true to report those as well. 
/* eslint unicorn/no-null: ["error", { "checkStrictEquality": true }] */

// Fail — strict equality against null is now reported
if (foo === null) {}

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Automatic exceptions

The following patterns are always allowed regardless of configuration:
PatternReason
Object.create(null)Creates a prototype-less object — a well-established pattern
useRef(null) / React.useRef(null)React ref initialization requires null
node.insertBefore(child, null)DOM API uses null as a sentinel to append at the end
This rule aligns with the TypeScript coding guidelines, which recommend using undefined and avoiding null.

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