(mongodb >=1.4.0)
MongoDB\BSON\Undefined::jsonSerialize — Returns a representation that can be converted to JSON
此函数没有参数。
Returns data which can be serialized by json_encode() to produce an extended JSON representation of the MongoDB\BSON\Undefined.
Note: The output is consistent with the MongoDB\BSON\toJSON() function, which uses the driver-specific legacy extended JSON format. This does not necessarily match the » relaxed or » canonical extended JSON representations used by MongoDB\BSON\toRelaxedExtendedJSON() and MongoDB\BSON\toCanonicalExtendedJSON(), respectively.