Excel Dir returns unexpected null - vba

Question

I'm trying to write what I thought would be a simple routine to take all the Excel sheets in a directory and copy them to tabs in a master sheet. Here's what I'm trying:
Sub GetSheets()
myPath = "C:\Users\Brian.Scott\Documents\2017_INVENTORY\TestInv"
Filename = Dir(myPath)
MsgBox (Filename)
Do While Filename <> ""
Workbooks.Open Filename:=myPath & Filename, ReadOnly:=True
For Each Sheet In ActiveWorkbook.Sheets
Sheet.Copy After:=ThisWorkbook.Sheets(1)
Next Sheet
Workbooks(Filename).Close
Filename = Dir()
Loop
End Sub
I put in the MsgBox when nothing was happening. It returns a null. myPath returns the correct name - which I copied and pasted from explorer to avoid spelling errors. I only have excel files in the directory, so I'm not error checking. This is a one-off need, but there are over 200 files in the directory, so I figured I could spend a little time on the code.
Any ideas will be greatly appreciated as I'm pretty green with this.

Answer 1

Declare all your variables - specify Option Explicit at the top of every module, and then declare every single variable you use until the code compiles again. Not doing that is only asking for trouble; VBA will happily compile and run a typo, and debugging that isn't fun at all. Use Option Explicit. Always.
Option Explicit
Public Sub GetSheets()
Const myPath As String = "C:\Users\Brian.Scott\Documents\2017_INVENTORY\"
Const myFilter As String = "TestInv*.xls?"
Dim myFilename As String
myFilename = Dir(myPath & myFilter)
Do While myFilename <> vbNullString
MsgBox myFilename
With Workbooks.Open(Filename:=myPath & myFilename, ReadOnly:=True)
Dim sh As Worksheet
For Each sh In .Worksheets
sh.Copy After:=ThisWorkbook.Sheets(1)
Next
.Close
End With
Filename = Dir
Loop
End Sub
Notice that With block - it's holding a reference to the Workbook object that the Workbooks.Open function returns, so you can do .Worksheets and .Close against it, without needing to code against ActiveWorkbook, and without needing to re-fetch that exact same object reference from the Workbooks collection at every iteration.
Your myPath contains a path, yes, but also wildcards, and I doubt this would work as expected:
Workbooks.Open "C:\Users\Brian.Scott\Documents\2017_INVENTORY\TestInv*.xls?\TestInv42.xlsx"
That's why I split the myPath string into a path and a filter: you supply the filter to the Dir function, and supply the Workbooks.Open function with the path with the file name that Dir returned.