{* ../../docs_src/body/tutorial001_py310.py hl[5:9] *}

与声明查询参数一样，包含默认值的模型属性是可选的，否则就是必选的。把默认值设为 `None` 可使其变为可选。

例如，上述模型声明如下 JSON "object"（即 Python `dict`）：

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

...由于 `description` 和 `tax` 是可选的（默认值为 `None`），下面的 JSON "object" 也有效：

```JSON
{
    "name": "Foo",
    "price": 45.2
}
```

		// should not happen
		t.Fatal(err)
	}
	if err := buf.UnreadByte(); err == nil {
		t.Fatal("UnreadByte: expected error, got nil")
	}
}

// verify that copying from an empty reader always has the same results,
// regardless of the presence of a WriteTo method.
func TestReaderCopyNothing(t *testing.T) {
	type nErr struct {
		n   int64
		err error
	}
	type justReader struct {

 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */

 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */

import jcifs.smb.SmbAuthException;

/**
 * This servlet may be used with pre-2.3 servlet containers
 * to protect content with NTLM HTTP Authentication. Servlets that
 * extend this abstract base class may be authenticated against an SMB
 * server or domain controller depending on how the
 * {@code jcifs.smb.client.domain} or {@code jcifs.http.domainController}
 * properties are be specified. <b>With later containers the

        // Act
        URLConnection conn = handler.openConnection(url);

        // Assert
        assertNotNull(conn);
        assertTrue(conn instanceof SmbFile, "Connection should be an instance of SmbFile");
        SmbFile file = (SmbFile) conn;
        assertEquals(url, file.getURL(), "Returned SmbFile should wrap the given URL");

 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */

 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific language
 * governing permissions and limitations under the License.
 */