ajaxorg/ace · error · TypeError

Cannot convert undefined or null to object

Error message

Cannot convert undefined or null to object

What it means

This TypeError is thrown by the ES6-shim polyfill for Object.assign when the first argument (target) is undefined or null. Per the ES6 spec, Object.assign cannot coerce null/undefined into an object, so the shim mimics native behavior and fails fast with this exact message.

Source

Thrown at src/lib/es6-shim.js:51

      var result = "";
      var string = this;
      while (count > 0) {
        if (count & 1) result += string;

        if ((count >>= 1)) string += string;
      }
      return result;
    });
  }
  if (!String.prototype.includes) {
    defineProp(String.prototype, "includes", function (str, position) {
      return this.indexOf(str, position) != -1;
    });
  }
  if (!Object.assign) {
    Object.assign = function (target) {
      if (target === undefined || target === null) {
        throw new TypeError("Cannot convert undefined or null to object");
      }

      var output = Object(target);
      for (var index = 1; index < arguments.length; index++) {
        var source = arguments[index];
        if (source !== undefined && source !== null) {
          Object.keys(source).forEach(function (key) {
            output[key] = source[key];
          });
        }
      }
      return output;
    };
  }
  if (!Object.values) {
    Object.values = function (o) {
      return Object.keys(o).map(function (k) {
        return o[k];

View on GitHub (pinned to 2c1eddc392)

Solutions

1. Ensure the target argument is a non-null object before calling Object.assign, or default it: Object.assign(target || {}, src)
2. Fix the upstream code that produced the null/undefined target instead of papering over it at the call site
3. If null targets are intentional no-ops in your logic, switch to a helper like {...target, ...src} or a merge utility that skips null targets
4. On modern engines verify Object.assign is native (not this shim) — the native one throws the same TypeError, so the root fix is identical

Example fix

// before
Object.assign(userPrefs, defaults); // userPrefs undefined on first run
// after
Object.assign(userPrefs || {}, defaults);

if (target == null) throw new TypeError('Object.assign requires a non-null target');
Object.assign(target, source);

function isMergeTarget(t) { return t !== null && (typeof t === 'object' || typeof t === 'function'); }

try {
  return Object.assign(target, src);
} catch (e) {
  if (e instanceof TypeError) return Object.assign({}, src); // or rethrow
  throw e;
}

When it happens

Trigger: Calling Object.assign(null, {...}) or Object.assign(undefined, {...}) — typically when a variable expected to hold a target object is uninitialized or a lookup returned null.

Common situations: Running code on legacy browsers (IE) or old JS engines lacking native Object.assign, where the es6-shim polyfill is active; passing the result of a failed lookup (e.g., map.get or DOM query) as the merge target.

AI-assisted analysis of ajaxorg/ace@2c1eddc392 (2026-08-30). Data as JSON: /api/errors/0df4957952d23b45. Report an issue: GitHub.