go/doc/next/6-stdlib/99-minor/encoding/json/45669.md

When marshaling, a struct field with the new omitzero option in the struct field tag will be omitted if its value is zero. If the field type has an IsZero() bool method, that will be used to determine whether the value is zero. Otherwise, the value is zero if it is the zero value for its type.

If both omitempty and omitzero are specified, the field will be omitted if the value is either empty or zero (or both).