requirednullable

Requirednullable is a data validation and schema design concept in which a field is required to be present in a data object, but its value may be null. This combination is used when the absence of the field is unacceptable, yet the semantic meaning of a missing value is not needed because null can carry deliberate meaning (for example, explicit "no value"). The exact behavior depends on the validation library or type system.

In JSON Schema, required is expressed as a list of property names, and the property defines a type that includes null. For example, a field middleName can be defined as type: ["string","null"] while middleName is listed in the required array. This enforces presence of the field while allowing its value to be either a string or null.

In many validation libraries, the same intent is expressed as required().nullable() or required().allow(null). In TypeScript, a runtime notion may be modeled with a union type like string | null and a separate constraint that the property exists.

Common use cases include API payloads where clients must send a field that may be null to signal a null value, database records where a column must be present but can be null, and forms where an input field should be present in the schema even if the user leaves it blank.

Common pitfalls include inconsistent handling of null across layers, default value substitution, and confusion between undefined and null. See also: nullable, required, optional fields.