VBA 函数 - 参数不可选

Public Function RETURN_Equipment(Optional category As String) As Collection
    Dim config As classConfiguration
    Set config = New classConfiguration

    Dim item As classItem
    Set item = New classItem

    Dim myCollection As Collection
    Set myCollection = New Collection

    For Each config In Configurations
        For Each item In config.colItems
            If IsMissing(category) Then   
                myCollection.add item
            ElseIf InStr(category, "mainframe") <> 0 And item.category = "mainframe" Then
                myCollection.add item
                MsgBox "Fired!"                
            ElseIf category = "accessory" And item.category = "accessory" Then
            Else
            End If
        Next
    Next

    RETURN_Equipment = myCollection
End Function

我不断得到

编译错误：
参数不可选

我在最后一行收到错误

RETURN_Equipment = myCollection

我理解错误消息，它告诉我我没有填写参数。但我只有一个参数，并且我已将其声明为可选。看起来代码认为我正在尝试从函数调用该函数？

是什么赋予了？

每当您分配一个对象时，您都需要使用set关键词。

set RETURN_Equipment = myCollection