GET Presence API result no space

Hi I want to ask why there is space_id empty in this result :

[0] => Array
(
[space_id] =>
[location_id] => 5842
[user_id] => 64605
[device_id] => 42176
[last_seen_at] => 2017-12-07T10:17:56+0000
[arrived_at] => 2017-12-07T10:17:56+0000
[expired_at] => 2017-12-07T10:18:07+0000
[session_ttl] => 510
[session_active] =>
)

[1] => Array
    (
        [space_id] => 25249
        [location_id] => 5842
        [user_id] => 64605
        [device_id] => 42176
        [last_seen_at] => 2017-12-07T10:17:32+0000
        [arrived_at] => 2017-12-07T10:17:32+0000
        [expired_at] => 2017-12-07T10:17:34+0000
        [session_ttl] => 510
        [session_active] => 
    )

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GET Presence API result no space_id