code: def GetCellValueNoFail (self, column, row = None):
                  
                  if row == None:
                          (row, column) = ParseCellSpec(column)
                  cell = GetCellValue(self, column, row)
                  if cell == None:
                          raise ValueError("cell %d:%d does not exist" % (column, row))
                  return cell
docs: get a cell, if it does not exist fail
                  note that column at row START AT 1 same as excel