docs: def find_field(self, field=None, alias=None):
          """
          Finds a field by name or alias.
  
          :param field: string of the field name or alias, dict of {'alias': field}, or a Field instance
          :type field: str or dict or Field
  
          :returns: The field if it is found, otherwise None
          :rtype: :class:`Field <querybuilder.fields.Field>` or None
          """
          if alias:
              field = alias
          field = FieldFactory(field, table=self, alias=alias)
          identifier = field.get_identifier()
          for field in self.fields:
              if field.get_identifier() == identifier:
                  return field
          return None