Silent Defaults — What Claude Gets Wrong

When data is missing, you silently substitute a default instead of surfacing the problem. The caller can't distinguish "no data" from "error." Bugs hide for weeks behind plausible-looking empty arrays and zero values.

The Core Rule

Missing required data is an error. Missing optional data is None/null. Neither is a default value.

REQUIRED field missing  →  Error (crash at startup, return error at runtime)
OPTIONAL field missing  →  None / null / Option::None
KNOWN SAFE default      →  Default (only when the default is genuinely correct)

Anti-Patterns You Default To