Empty array removed from XML serialization

[niabot]

Q	A
Bug report?	yes
Feature request?	no
BC Break report?	no
RFC?	no

Steps required to reproduce the problem

If i serialize the following following class (i removed the other properties) then the roles property is removed from the XML. But it stays if i serialize to JSON or YAML.

namespace app\controllers\login;

use JMS\Serializer\Annotation as SE;

/**
 * @SE\XmlRoot("loginResponse")
 */
class LoginResponseObject {
    	/**
	 * @SE\Type("array<string>")
	 * @SE\XmlList(inline=false,entry="role")
	 */
	public $roles = [];
}

As JSON i get:

{
  "roles": []
}

But as XML i only get:

<?xml version="1.0" encoding="UTF-8"?>
<loginResponse>
</loginResponse>

I would expect the following output, which would match the results for JSON and YAML:

<?xml version="1.0" encoding="UTF-8"?>
<loginResponse>
    <roles></roles>
</loginResponse>

[goetas]

see

serializer/src/JMS/Serializer/Annotation/XmlCollection.php

Line 41 in ef6000e

public $skipWhenEmpty = true;

[niabot]

This property should be added to the annotation documentation. I totally missed it.

[goetas]

PR are welcome