For each loop

Can someone tell me why 'j' in my code below returns as "empty"?

Public Sub CreateChart()

Dim chartDataSheets() As Long
Dim numberCells As Integer
Dim arraySize As Integer
Dim i As Integer
Dim j As Variant
Dim chartData As Range
Dim Inp As String


With Application

.ScreenUpdating = False

Let Inp = ThisWorkbook.Sheets("CreateChart").Cells(3, 2).Value

Workbooks.Open (Inp)

numberCells = WorksheetFunction.CountA(ThisWorkbook.Worksheets("CreateChart").Columns(4)) + 1

arraySize = (numberCells - 2)

ReDim chartDataSheets(arraySize)

For i = 3 To numberCells

chartDataSheets((i - 2)) = ThisWorkbook.Worksheets("CreateChart").Cells(i, 4).Value

Next i

'MsgBox chartDataSheets(1)
'MsgBox chartDataSheets(2)

For Each j In chartDataSheets

ActiveWorkbook.Worksheets(j).Activate

chartData = ActiveWorkbook.Worksheets(j).UsedRange.Select

Next j

End With

End Sub