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## 1.57.3

**`(fix):`** Omit global headers (declared under `api.headers`) from requests when they are
left unset, instead of sending them with an empty value. This matches the
behavior of auth scheme headers, which were already guarded. This applies to
string, UUID, bytes, date, datetime, and enum headers; boolean and numeric
headers are unchanged, since `false` and `0` are meaningful values that
cannot be distinguished from an unset field. Unset UUID, date, and datetime
headers are no longer sent as `00000000-0000-0000-0000-000000000000` and
`0001-01-01` either.