The WMI interface cannot retrieve data of array type

Question

I encountered an error while calling the Method of classes in the WMI interface to retrieve array type data from BIOS. My MOF description file contains the following content:

[WMI,
Dynamic,
Provider("WmiProv"),
Locale("MS\\0x409"),
Description("Call BIOS Function through WMI"),
guid("{B66BC8B8-8DE4-4990-B8C8-F73DFF82FF9A}")
]
class OemWMIMethodC
{
[key, read]
string InstanceName;
[read] boolean Active;
[WmiMethodId(1),
Implemented,
read, write,
Description("OEM WMI Function")
] void OemWMIfunC([in, Description("Test2")] uint64 Data, [out, MAX(256)]uint8 u8Output[]);
};

The error message is as follows:

Invoke-CimMethod : Invalid object
At E:\test01.ps1:8 char:10
+     $r = Invoke-CimMethod -InputObject $i -MethodName OemWMIfun -Argu ...
+          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (OemWMIMethod (I...0C14\EmdWmi_0"):CimInstance) [Invoke-CimMethod], CimExc
   eption
    + FullyQualifiedErrorId : HRESULT 0x8004100f,Microsoft.Management.Infrastructure.CimCmdlets.InvokeCimMethodCommand

=== Results ===
[ERROR] Cannot index into a null array.

I ensured through debugging that the Method in the ASL file in the BIOS was executed to the Return (Buffer) step, and I tried to set the buffer size to 256, 80, 64, and 8, but this issue occurred. And when I change the data type defined in MOF from an array of type uin8 to uint64, it can be executed correctly and the data can be obtained. Why is this?