HPワイヤレスボタン、ACPI WLBU AE_NOT_FOUND

デバイスとメソッドの両方が定義されている場合、「AE_NOT_FOUND」が発生するのはなぜですか？

dmesgエラー：

[    9.925882] ACPI Error: [WLVD] Namespace lookup failure, AE_NOT_FOUND (20160422/psargs-359)
[    9.927455] ACPI Error: Method parse/execution failed [\_SB.WLBU._STA] (Node ffff8803ee8b40c8), AE_NOT_FOUND (20160422/psparse-542)

データ転送時間：

// http://h30434.www3.hp.com/t5/Notebook-Hardware-and-Upgrade-Questions/HP-250-G2-Unknown-Device-ACPI-HPQ6001/td-p/5056511
// hp wireless button...
// hp_wmi && hp_wireless are loaded...
// 
// [    0.744110] ACPI Error: [WLVD] Namespace lookup failure, AE_NOT_FOUND (20160422/psargs-359)
// [    0.744123] ACPI Error: Method parse/execution failed [\_SB.WLBU._STA] (Node ffff8803ee8b40c8), AE_NOT_FOUND (20160422/psparse-542)
//
    Device (WLBU)
    {
        Name (_HID, EisaId ("HPQ6001"))  // _HID: Hardware ID
        Name (WLDP, 0xFF)
        Method (_STA, 0, NotSerialized)  // _STA: Status
        {
            If ((WLDP == 0xFF))
            {
                Local0 = Zero
                OSTP ()
                If ((((OSYS == 0x07DC) || (OSYS == 0x07DD)) || (OSYS == 0x07DF)))
                {
                    If (((WLVD != Zero) && (WLVD != 0xFFFF)))
                    {
                        Local0 = 0x0F
                    }
                }

                WLDP = Local0
            }

            Return (WLDP) /* \_SB_.WLBU.WLDP */
        }

    }