Normalize the "fields" argument to most find methods

def _param_fields(kwargs, fields):
  """
    Normalize the "fields" argument to most find methods
  """
  if fields is None:
    return
  if type(fields) in [list, set, frozenset, tuple]:
    fields = {x: True for x in fields}
  if type(fields) == dict:
    fields.setdefault("_id", False)
  kwargs["projection"] = fields