Handle absence/unsupported data explicitly and defensively: return `None` (or a clear error) when a value cannot be produced faithfully, and don’t “auto-fix” by inventing defaults, creating missing prerequisites, or silently dropping problematic entries. This prevents misleading “success” states and subtle contract violations. Guidelines: - For unsupported fallback targets, use `Option` and return `None` instead of substituting misleading values. - For missing prerequisites/config directories, treat it as “not installed / not supported” and fail rather than creating directories and continuing. - When converting/serializing potentially-null/invalid data (e.g., platform-specific encoding), fail early if the representation can’t be preserved; never silently drop entries that change semantics. Example pattern (Rust): ```rust pub(crate) fn hostname() -> Option { // Return None when the fallback target is unsupported None } pub(crate) fn install_agent() -> std::io::Result<()> { let dir = agent_config_dir()?; if !dir.is_dir() { return Err(std::io::Error::other(format!( "agent config directory not found at {}. install agent first", dir.display() ))); } // Only proceed when the prerequisite truly exists Ok(()) } fn serialize_env_entry(value: &OsStr) -> std::io::Result { // If the platform serialization cannot represent the value faithfully, // return an error instead of dropping it. Err(std::io::Error::other("cannot faithfully serialize environment value")) } ```