import org.dbflute.cbean.ConditionBean;
import org.dbflute.cbean.result.ListResultBean;
import org.dbflute.cbean.result.PagingResultBean;
import org.dbflute.exception.IllegalBehaviorStateException;
import org.dbflute.optional.OptionalEntity;
import org.dbflute.util.DfTypeUtil;
import org.opensearch.action.bulk.BulkRequestBuilder;
import org.opensearch.action.delete.DeleteRequestBuilder;
import org.opensearch.action.index.IndexRequestBuilder;

import org.codelibs.fess.exception.UserRoleLoginException;
import org.codelibs.fess.helper.CrawlingConfigHelper;
import org.codelibs.fess.helper.PermissionHelper;
import org.codelibs.fess.util.ComponentUtil;
import org.dbflute.optional.OptionalThing;
import org.lastaflute.di.util.LdiFileUtil;
import org.lastaflute.web.login.LoginManager;
import org.lastaflute.web.response.ActionResponse;
import org.lastaflute.web.ruts.process.ActionRuntime;

import org.codelibs.fess.storage.StorageClientFactory;
import org.codelibs.fess.storage.StorageItem;
import org.codelibs.fess.util.ComponentUtil;
import org.codelibs.fess.util.RenderDataUtil;
import org.dbflute.optional.OptionalThing;
import org.lastaflute.web.Execute;
import org.lastaflute.web.response.ActionResponse;
import org.lastaflute.web.response.HtmlResponse;
import org.lastaflute.web.response.StreamResponse;

          .put(CharMatcher.class, CharMatcher.none())
          .put(Joiner.class, Joiner.on(','))
          .put(Splitter.class, Splitter.on(','))
          .put(com.google.common.base.Optional.class, com.google.common.base.Optional.absent())
          .put(Predicate.class, Predicates.alwaysTrue())
          .put(Equivalence.class, Equivalence.equals())
          .put(Ticker.class, Ticker.systemTicker())

			// then it is implicit on for the sub-system.
			enabled = true
		}
		v, _ := currKVS.Lookup(hkv.Key)
		if v == "" && !hkv.Optional && enabled {
			// Return error only if the
			// key is enabled, for state=off
			// let it be empty.
			return false, Errorf(
				"'%s' is not optional for '%s' sub-system, please check '%s' documentation",
				hkv.Key, subSys, subSys)
		}
	}
	c[subSys][tgt] = currKVS

Assim como quando declaramos parâmetros de consulta, quando um atributo do modelo possui um valor padrão, ele se torna opcional. Caso contrário, se torna obrigatório. Use `None` para torná-lo opcional.

Por exemplo, o modelo acima declara um JSON "`object`" (ou `dict` no Python) como esse:

```JSON
{
    "name": "Foo",
    "description": "An optional description",
    "price": 45.2,
    "tax": 3.5
}
```

import org.codelibs.fess.util.ComponentUtil;
import org.codelibs.fess.util.DocumentUtil;
import org.codelibs.fess.util.QueryResponseList;
import org.dbflute.optional.OptionalEntity;
import org.dbflute.optional.OptionalThing;
import org.lastaflute.web.util.LaRequestUtil;
import org.opensearch.action.update.UpdateRequest;
import org.opensearch.script.Script;

	list *LruList[K, V]

	// The LRU Key of this element.
	Key K

	// The Value stored with this element.
	Value V

	// The time this element would be cleaned up, optional
	ExpiresAt time.Time

	// The expiry bucket item was put in, optional
	ExpireBucket uint8
}

// PrevEntry returns the previous list element or nil.
func (e *Entry[K, V]) PrevEntry() *Entry[K, V] {

import org.dbflute.cbean.ConditionBean;
import org.dbflute.cbean.result.ListResultBean;
import org.dbflute.cbean.result.PagingResultBean;
import org.dbflute.exception.IllegalBehaviorStateException;
import org.dbflute.optional.OptionalEntity;
import org.dbflute.util.DfTypeUtil;
import org.opensearch.action.bulk.BulkRequestBuilder;
import org.opensearch.action.delete.DeleteRequestBuilder;
import org.opensearch.action.index.IndexRequestBuilder;

import org.dbflute.cbean.ConditionBean;
import org.dbflute.cbean.result.ListResultBean;
import org.dbflute.cbean.result.PagingResultBean;
import org.dbflute.exception.IllegalBehaviorStateException;
import org.dbflute.optional.OptionalEntity;
import org.dbflute.util.DfTypeUtil;
import org.opensearch.action.bulk.BulkRequestBuilder;
import org.opensearch.action.delete.DeleteRequestBuilder;
import org.opensearch.action.index.IndexRequestBuilder;