PHP warning: "unserialize() expects parameter 1 to be string, array given"

[texttheater]

This is the content of the server response when I try to use the create/post API method:

{"data":"true","error":null}<br />\n<b>Warning</b>:  unserialize() expects parameter 1 to be string, array given in <b>/path/to/my/SmfRestServer.php</b> on line <b>397</b><br />\n<br />\n<b>Warning</b>:  unserialize() expects parameter 1 to be string, array given in <b>/path/to/my/SmfRestServer.php</b> on line <b>398</b><br />\n<br />\n<b>Warning</b>:  unserialize() expects parameter 1 to be string, array given in <b>/path/to/my/SmfRestServer.php</b> on line <b>399</b><br />\n

With the original version of the API, I don’t get the warnings. I’m mystified because I don’t see anything in SmfRestServer.php that might already have unserialized the parameters. Any ideas why this might be happening?