Button style API is not defined, example codes from tutorial are broken

[XiaoGuo, Liu]

I just copied the code snippet at https://developer.ubuntu.com/api/apps/qml/sdk-15.04.5/Ubuntu.Components.StyledItem/, I get the error like http://paste.ubuntu.com/16123241/

QML debugging is enabled. Only use this in a safe environment.
qml: Page_QMLTYPE_17(0xa86bd0)"test page": In Ubuntu.Components 1.3, the use of Page.title, Page.flickable and Page.head is deprecated. Use Page.header and the PageHeader component instead.
file:///usr/ubuntu-sdk-dev/qml/Ubuntu/Components/1.3/Button.qml:108:25: Unable to assign [undefined] to QFont
file:///usr/ubuntu-sdk-dev/qml/Ubuntu/Components/1.3/Button.qml:103:33: Unable to assign [undefined] to QQuickGradient*
file:///usr/ubuntu-sdk-dev/qml/Ubuntu/Components/1.3/Button.qml:92:27: Unable to assign [undefined] to QColor

The example code is at https://github.com/liu-xiao-guo/style

The code snippet at the link https://developer.ubuntu.com/api/apps/qml/sdk-15.04.4/UbuntuUserInterfaceToolkit.ubuntu-theming-styles/ also has the same problem.

Button {
    id: button
    style: Rectangle {
        implicitWidth: units.gu(12)
        implicitHeight: units.gu(5)
        color: styledItem.color
        border {
            width: units.dp(1)
            color: styledItem.strokeColor
        }
        Label {
            text: styledItem.text
            font: styledItem.font
        }
    }
}

Thanks & best regards,
XiaoGuo