Add support set in fields stdClass in Structure::prepareToStore

[MCubs]

Hello,

I created a patch that adds the ability to save an empty object to the collection.
This need arose due to the nature of my system.
The save method in the class Document saves an empty object as an array.
Playback example:
I have Model Car extended Document.
Create $car = new Car();
$car->set('human-id', 1)->save();
$car->update(["human-id" => 1], ['$set' =>["markets-data.1" => ["car" => 1]]]);
Data in DB:

{
	"_id" : ObjectId(""),
	"markets-data" : {
		"1" : {"car": 1}
	},
	"human-id" : 1
}

$car->update(["human-id" => 1], ['$unset' =>["markets-data.1" => ["car" => 1]]]);
Data in DB:

{
	"_id" : ObjectId(""),
	"markets-data" : {},
	"human-id" : 1
}

$car->save();
Data in DB:

{
	"_id" : ObjectId(""),
	"markets-data" : array(),
	"human-id" : 1
}

Here is an example of how update works in the native view:

> db.vehicle.update({"human-id": 36}, {'markets-data': {}, "human-id": 36});
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })
> db.vehicle.find({"human-id": 36}, {'markets-data': 1, 'human-id': 1}).pretty();
{
	"_id" : ObjectId(""),
	"markets-data" : {},
	"human-id" : 36
}

How to use my patch:
Create $car = new Car();
$car->set('human-id', 1)->save()
Data in DB:

{
	"_id" : ObjectId(""),
	"human-id" : 1
}

$car->set('markets-data', new \stdClass)->save();
{
"_id" : ObjectId(""),
"markets-data" : {},
"human-id" : 1
}

[sokil]

https://travis-ci.org/sokil/php-mongo/builds/484386828

[sokil]

you broke tests

[sokil]

i thought that was dejawoo but #143 there is already closed issue with same pull request )))

[sokil]

#143

There is problem how to identify is this empty object {} or list []

And there is a reason to specify types #144

[sokil]

i thought that was dejawoo but #143 there is already closed issue with same pull request )))

[MCubs]

When i can get instruction for run docker?

[sokil]

When? Now! https://github.com/sokil/php-mongo#docker-phpunit-tests )