How to skip empty sheet?

[VAer]

Runtime error 1004, No cells found. Since there is a empty sheet (a sheet with nothing)

Below is just sample code.

Sub removeextraspace()

Dim WS As Worksheet
Dim WB As Workbook
Dim aCell As Range

Application.ScreenUpdating = False

ThisWorkbook.Sheets(1).Cells(20, 2).Value = "    Hi   Hi   "
ThisWorkbook.Sheets(2).Cells(20, 3).Value = "    XYZ   XYZ   "

For Each WS In ThisWorkbook.Worksheets
    For Each aCell In WS.UsedRange.SpecialCells(xlCellTypeConstants)
        aCell = WorksheetFunction.Trim(aCell)
    Next aCell
Next

Application.ScreenUpdating = True


End Sub