code: def _check_and_update_params(self, required, params):
          
          for r in required:
              if r not in params:
                  raise PayPalError("Missing required param: %s" % r)
  
          # Upper case all the parameters for PayPal.
          return (dict((k.upper(), v) for k, v in params.items()))
docs: Ensure all required parameters were passed to the API call and format
          them correctly.