code: def set_str_param(params, name, value):
      
      if value is None:
          return
  
      if isinstance(value, str):
          params[name] = value
      elif isinstance(value, unicode):
          params[name] = value.encode('utf-8')
      else:
          raise ValueError("Parameter '%s' must be a string or None, got %r." % (
              name, value))
docs: Set a string parameter if applicable.
  
      :param dict params: A dict containing API call parameters.
  
      :param str name: The name of the parameter to set.
  
      :param value:
          The value of the parameter. If ``None``, the field will not be set. If
          an instance of ``str``, the relevant field will be set. If an instance
          of ``unicode``, the relevant field will be set to the UTF-8 encoding.
          Any other value will raise a `ValueError`.
  
      :returns: ``None``