Return {} as empty object instead of empty array

[thekid]

...and be consistent with emitting empty objects as {}.

Before

Emitting an empty object as JSON after reading it results in it being output as an empty array:

$ xp -w 'use text\json\Json; Json::of(Json::read("{}"))'
[]

# There is no problem with non-empty objects though!
$ xp -w 'use text\json\Json; Json::of(Json::read("{\"key\":\"value\"}"))'
{"key":"value"}

After

Consistent result:

$ xp -w 'use text\json\Json; Json::of(Json::read("{}"))'
{}

Potential pitfalls

Objects (even ones without a single property) are never considered empty:

empty([]);         // true
empty((object)[]); // false

Also, using sizeof() will raise the following exception: lang.Error (sizeof(): Argument 1 ($value) must be of type Countable|array, stdClass given) - similar to all cases where we use type hints; which would then need to be widened to the (ugly-looking) array|stdClass to support this.

See also

• https://www.php.net/manual/en/json.constants.php#constant.json-object-as-array
• https://stackoverflow.com/questions/8595627/best-way-to-create-an-empty-object-in-json-with-php
• Invalid json handling of empty objects {} converted to empty arrays [] FriendsOfSymfony/FOSRestBundle#980

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⚠️ Heads up: This is a BC break and would require a major version release, 6.0 at the time of writing.