Null/undefined safety should prevent crashes and preserve correct semantics. Don’t hide missing required inputs with optional chaining or weak fallbacks.

Standards

1. Validate required dependencies explicitly: If an object (e.g., themeVariables) is expected to exist, check it and emit a warning/error when it’s missing instead of silently continuing.
2. Use type-correct defaults, not null sentinels: If downstream code expects a color/string/number/boolean, provide a real default of that type—avoid ?? null unless the API explicitly supports null.
3. Avoid truthiness logic that changes meaning: Watch for patterns like value || true (it always becomes true). Compute booleans with correct precedence.
4. Be intentional about null vs undefined: Use ?? when you only want to treat null/undefined as “missing”, and add explicit branches when precedence matters.

Example pattern

function getThemeValue<T>(theme: any, key: string, fallback: T): T {
  if (!theme) {
    console.warn(`Missing themeVariables; using fallback for ${key}`);
    return fallback;
  }
  const value = theme[key];
  if (value === undefined || value === null) {
    console.warn(`Missing theme value ${key}; using fallback`);
    return fallback;
  }
  return value as T;
}

const quadrant1Fill = getThemeValue(themeVariables, 'quadrant1Fill', '#000000');

// Boolean example: avoid `anything || true`
const useHtmlLabels = node.useHtmlLabels ?? evaluate(config.htmlLabels ?? undefined) ?? true;

Applying these rules makes UI/config failures easier to diagnose, avoids runtime surprises from invalid sentinel values, and keeps boolean/null semantics correct.