prefer existence over truthiness

Use explicit existence checks instead of truthiness checks when dealing with object properties, null/undefined values, or when falsy values are valid data.

Truthiness checks can cause bugs in several scenarios:

1. Object properties containing objects/promises - These are always truthy even when you want to check existence
2. Falsy but valid values - Values like 0, "", or false that should be processed but fail truthiness checks
3. Null vs undefined distinction - When you need to handle both null and undefined consistently

Examples:

// ❌ Bad: Promise objects are always truthy
if (fileProcessors[filePath]) {
  return fileProcessors[filePath]
}

// ✅ Good: Check for property existence
if (filePath in fileProcessors) {
  return fileProcessors[filePath]
}

// ❌ Bad: Filters out valid falsy values like "0"
return trim ? dequote(_.trim(result)) : result

// ✅ Good: Only filter out null/undefined
return trim && result != null ? dequote(_.trim(result)) : result

// ❌ Bad: Boolean true is falsy in this context check
if (keyEntry === undefined) {
  // handle undefined case
}

// ✅ Good: Explicit check avoids confusion with boolean values
if (!keyEntry) {
  // This would incorrectly trigger for boolean false
}

Use in operator for object property existence, != null for null/undefined checks when falsy values are valid, and be explicit about what condition you’re actually testing for.