- optionalField<K, VI, VO>(key, $value): $.Shape<$.Expand<Readonly<Partial<Record<K, VI>>>>, $.Expand<Partial<Record<K, VO>>>>
 Type Parameters
- K extends string | number | symbol
 - VI
 - VO
 
Returns $.Shape<$.Expand<Readonly<Partial<Record<K, VI>>>>, $.Expand<Partial<Record<K, VO>>>>