code: def nulls_first(col, session: Session) -> dict[str, Any]:
      """Specify *NULLS FIRST* to the column ordering.
  
      This is only done to Postgres, currently the only backend that supports it.
      Other databases do not need it since NULL values are considered lower than
      any other values, and appear first when the order is ASC (ascending).
      """
      if session.bind.dialect.name == "postgresql":
          return nullsfirst(col)
      else:
          return col
  
imports: from __future__ import annotations
  import contextlib
  import copy
  import datetime
  import json
  import logging
  from typing import TYPE_CHECKING, Any, Generator, Iterable, overload
  from dateutil import relativedelta
  from sqlalchemy import TIMESTAMP, PickleType, event, nullsfirst, tuple_
  from sqlalchemy.dialects import mysql
  from sqlalchemy.types import JSON, Text, TypeDecorator
  from airflow.configuration import conf
  from airflow.serialization.enums import Encoding
  from airflow.utils.timezone import make_naive, utc
label_desc: Use image node_id 5 for calling a global function with example usage: nulls_first(col, session) and returns: nullsfirst, col