docs: def safe_date(self, x):
          """Transform x[self.col_name] into a date string.
  
          Args:
              x(dict like / pandas.Series): Row containing data to cast safely.
  
          Returns:
              str
          """
  
          t = x[self.col_name]
          if np.isnan(t):
              return t
  
          elif np.isposinf(t):
              t = sys.maxsize
  
          elif np.isneginf(t):
              t = -sys.maxsize
  
          tmp = time.localtime(float(t) / 1e9)
          return time.strftime(self.date_format, tmp)