def cvtInt(intstr):
  """ Convert integer string into integer.
    
      Parameters:
        intstr - integer string
                   format: "[0-9]+"

      Return Value:
        Returns converted integer value on success. None on error.
  """
  try:
    val = int(intstr)
    return val
  except (SyntaxError, NameError, TypeError, ValueError):
    return None