Sign Flip Macro To Skip Blanks

I have been using this macro, which works perfect:


Sub Signflip()
Dim cell As Range
For Each cell In Selection
If IsNumeric(cell.Value) Then cell.Value = -cell.Value
Next cell
End Sub

It allows me to select cells and flip from neg to pos, pos to neg, and it won't error out on text cells. Great little macro.

However, I don't like how it puts a zero in blank cells. It slows down the macro when I select large areas. Is there a way to make this macro work the same way but skip over empty or blank cells and not enter a zero.