Bug Report

Equal.equals throws TypeError: Cannot convert undefined or null to object when comparing values where one is null and the other is a non-null object, inside a structuralRegion.

Reproduction

import * as Equal from "effect/Equal"
import * as Utils from "effect/Utils"

// This crashes:
Utils.structuralRegion(() => Equal.equals({ name: "hello" }, null))
// TypeError: Cannot convert undefined or null to object
//   at Object.getPrototypeOf (<anonymous>)
//   at compareBoth (Equal.ts)

Root Cause

In compareBoth, when selfType === "object":

1. Line checking self !== null && that !== null correctly prevents entering the first block when one is null
2. But it falls through to the structuralRegionState.enabled block
3. Object.getPrototypeOf(self) is called without a null guard — crashes when self is null

This is because typeof null === "object" in JavaScript, so null passes the type check but then Object.getPrototypeOf(null) throws.

Suggested Fix

Add a null guard before the getPrototypeOf calls:

if (structuralRegionState.enabled) {
  if (self === null || that === null) {
    return false;
  }
  // ... rest of structural comparison
}

Environment

• effect@3.20.0
• Discovered when using structural equality comparison on form state objects containing nullable fields