Explicit Null Semantics

When handling optional/nullable values in TypeScript/React, make “unset/default” distinct from “legitimate empty/zero” and avoid truthiness-based guards.

Apply: 1) Use a dedicated sentinel for “never set”

• Prefer null/undefined to represent “unset”, especially when 0, '', or false are meaningful. 2) Check explicitly for sentinel/optionals
• Prefer value !== undefined / value != null over if (value) when the value may be 0 or ''. 3) Normalize before branching
• For user input, normalize (trim) before deciding which code path applies. 4) Validate using the intended combined condition
• Compute derived state first, then apply the combined predicate.

Example (sentinel + explicit checks):

// Sentinel models “never set” separately from a real 0.
const [navExpandedWidth, setNavExpandedWidth] = useState<number | null>(null);

useEffect(() => {
  window.electron.getSetting('navExpandedWidth').then((stored: number | null) => {
    if (stored === null) {
      // keep component default
      return;
    }

    // stored === 0 is a legitimate explicit value, not “unset”
    setNavExpandedWidth(stored);
  });
}, []);

// Explicit optional check (don’t rely on truthiness)
const initialMessage = editedMessage !== undefined
  ? { msg: editedMessage, images: [] }
  : undefined;

This prevents bugs where guards accidentally skip applying valid persisted values (e.g., 0) or mis-handle empty-but-present content (e.g., '').