When data is optional/unknown, handle it intentionally and explicitly—either skip the feature (return `None`) or fall back to a safe default—never via implicit drop or placeholder sentinel values. Standards: 1) Use `Option` (or “unset” fields) to represent missingness. Don’t encode “missing user” as an empty string; use `Option` (or clear the field) instead. 2) For optional features: return `None` when the input is absent or invalid (e.g., empty/unparseable config) so you don’t inject placeholder context. 3) For UX that must keep working: when an identifier can’t be resolved (unknown profile/name), fall back to a defined default rather than aborting. 4) Enforce invariants in types: if `None` should never occur, remove `Option` from parameters/fields and make it impossible to construct invalid states. 5) Be explicit in branching: enumerate all enum/location/type cases so non-local/null/unknown cases don’t get silently mishandled. Example pattern (skip-or-fallback): ```rust fn resolve_profile(agent_profile_name: Option<&str>, default_profile: &str) -> Option<&str> { match agent_profile_name { None => Some(default_profile), Some(name) if is_known_profile(name) => Some(name), Some(_unknown) => { // Unknown should still resolve to something usable. Some(default_profile) } } } fn load_optional_context(path: &Path) -> Option { let content = path.read_to_string().ok()?; // absent/IO error => None if content.trim().is_empty() { return None; // invalid/empty config => None (don’t inject placeholders) } Some(content) } ```