Salesforce PHP API : Creating folder

Question

I am getting error when trying to create a document folder in Salesforce using PHP toolkit. Below is the code that I used.

$createFolderFields = array ('name' => $sf_folder_name,
                                            'fullName' => 'X' . $sf_folder_name,
                                            'DeveloperName' => 'X' . $sf_folder_name,
                                            'Type' => 'Document',
                                            'accessType' => 'Shared');

                $documentFolder                 = new stdclass();
                $documentFolder->fields         = $createFolderFields;
                $documentFolder->type           = 'Folder';
                $responseFolderCreate = $mySforceConnection->create($documentFolder);
                print_r($documentFolder);
                print_r($responseFolderCreate);
                exit;

The values returned and error message is as follows

    stdClass Object
(
    [fields] => Array
        (
            [name] => 6000155Document
            [fullName] => X6000155Document
            [DeveloperName] => X6000155Document
            [Type] => Document
            [accessType] => Shared
        )

    [type] => Folder
)
Array
(
    [0] => stdClass Object
        (
            [errors] => Array
                (
                    [0] => stdClass Object
                        (
                            [fields] => Array
                                (
                                    [0] => DeveloperName
                                )

                            [message] => Folder Unique Name must be provided.: Folder Unique Name
                            [statusCode] => FIELD_INTEGRITY_EXCEPTION
                        )

                )

            [id] => 
            [success] => 
        )

)