setValidationGroup() expects a list of valid input names - php

Question

I am trying to send a PATCH request through cURL and i get this response:
HTTP/1.1 400 Bad Request Server: nginx Date: Fri, 01 Apr 2016 09:16:03 GMT Content-Type: application/problem+json Content-Length: 198 Connection: keep-alive X-Powered-By: PHP/5.6.19 {"type":"http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html","title":"Internal Server Error","status":500,"detail":"setValidationGroup() expects a list of valid input names; \"\" was not found"}
My code:
sendData("2016-10-01", "2016-10-02", "1234");
function sendData($from, $to, $property){
$data = array(
"from" => $from,
"to" => $to,
"booking_id" => 3
);
$data = json_encode($data);
echo $data . "<br>";
$url = "https://api.urlhost.com/property/".$property."/avail";
echo $url. "<br>";
$headers = array('Authorization: Basic dGVhQGJsdW1lbnJpdmllcmEuOIT6Qmx1bQVucm17aAKyzTtyfw==','Content-Type: application/json-patch+json');
$curl = curl_init();
curl_setopt($curl, CURLOPT_URL, $url);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, 0);
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, 0);
curl_setopt($curl, CURLOPT_CUSTOMREQUEST, 'PATCH');
curl_setopt($curl, CURLOPT_POSTFIELDS, $data);
curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);
curl_setopt($curl, CURLOPT_HEADER, true);
$response = curl_exec($curl);
echo ($response) . PHP_EOL;
//print_r(curl_getinfo($ch));
curl_close($curl);
}
When i echo the data and url i get these:
{"from":"2016-10-01","to":"2016-10-02","booking_id":3}
https://api.urlhost.com/property/1234/avail
But still is giving me this error. Any suggestions why this might happen?