vb.net - Check if cell if empty -

I am trying to check if the cell (A5) is empty in the sheet tstDash, currently there is a formula in the cell But sometimes the result is empty and sometimes there is a number.

If it is empty, then I need a message box. Otherwise do other things.

I have this code, but it is completely ignoring the line and it fits me.

  if chk25thPercentile.Checked = True and Globals.tsdDash.Range ("A5"). Value is DBNull.Value    
 
 
 Try it.  
 < Code> if chk25th per second Checked and IsDBNull (Globals.T.TdDash.Range ("A5"). Value)