how to avoid null/double click

Hi there, the below event macro creates a line above the cell entry in column A.

It also creates a line if i double click in cell which i don not want. I just want a line to be created if a number entered in any cell of column A

Could some one help me..thanks-var

Private Sub Worksheet_Change(ByVal Target As Range)
    If Not Intersect(Range("A1:B400"), Target) Is Nothing Then
        If IsNumeric(Target.Cells(1, 1)) Then
       
            Range("A" & Target.Row & ":J" & Target.Row).Borders(xlEdgeTop).Weight = xlMedium
           
        End If
    End If