VBA函数检查工作簿是否存在

我有两本工作手册1:Source.xlsx和2。Destination.xlsx。如果#2与#1位于同一位置，则将工作簿返回到我的主函数，否则创建一个新工作簿并返回它。 我有以下代码：

Function CheckForExistingWorkbooks() As Workbook
Dim wb1 As Workbook
Dim FilePath As String
Dim TestStr As String

FilePath = ThisWorkbook.Path & "\Student Information.xlsx"

TestStr = ""
On Error Resume Next
TestStr = Dir(FilePath)
On Error GoTo 0
If TestStr = "" Then
    Set wb1 = Workbooks.Add
Else
    Set wb1 = Workbooks.Open(FilePath)
End If

CheckForExistingWorkbooks = wb1
End Function 

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调试时，函数返回“Nothing”。如何使其工作？

尝试此方法-无需错误检测：

Function CheckForExistingWorkbooks() As Workbook
    Dim wb1 as Workbook
    Dim TestStr As String, FilePath As String
    FilePath = ThisWorkbook.Path & "\Student Information.xlsx"
    If Len(Dir(FilePath)) = 0 Then
        Set wb1 = Workbooks.Add
    Else
        Set wb1 = Workbooks.Open(FilePath)
    End If
    Set CheckForExistingWorkbooks = wb1
End Function

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使用Set-CheckForExistingWorkbook=wb1