Whether an object property using this codec must occur in the input.
The default is false. Deser.require_input enables this check: an absent property then raises Deser.Error.MISSING_REQUIRED. An explicit null is different from an absent property; reject null separately with Deser.reject_null. To require both, use Deser.require_input (Deser.reject_null (codec)). This flag applies to object properties, not collection elements. For example, require_input (new StringCodec ()) rejects an absent property but still accepts an explicit null. Wrap the StringCodec with Deser.reject_null as well to reject both cases.