Flujo de aire – seleccione los datos de la tabla de BigQuery en un marco de datos.

Estoy intentando ejecutar el siguiente DAG en Airflow Composer en Google Cloud y sigo obteniendo el mismo error:
El conn_id hard_coded_project_name no está definido.

¿Puede alguien dirigirme hacia la dirección correcta?

from airflow.models import DAG 
import os

from airflow.operators.dummy import DummyOperator
from airflow.operators.bash_operator import BashOperator
from airflow.operators.python_operator import PythonOperator

import datetime
import pandas as pd

from airflow.contrib.operators.gcs_to_bq import GoogleCloudStorageToBigQueryOperator
from airflow.contrib.operators.bigquery_operator import BigQueryOperator

from airflow.providers.google.cloud.operators import bigquery
from airflow.contrib.hooks.bigquery_hook import BigQueryHook

default_args = {
    'start_date': datetime.datetime(2020, 1, 1),
}

PROJECT_ID = os.environ.get("GCP_PROJECT_ID", "hardcoded_project_name")

def list_dates_in_df():
            hook = BigQueryHook(bigquery_conn_id=PROJECT_ID,
                                 use_legacy_sql=False)
            bq_client = bigquery.Client(project = hook.get_field("project"),
                                         credentials = hook.get_credentials())
            query = "select count(*) from LP_RAW.DIM_ACCOUNT;"
            df = bq_client.query(query).to_dataframe()

with DAG(
        'df_test',
        schedule_interval=None,
        catchup = False,
        default_args=default_args
        ) as dag:

    list_dates = PythonOperator(
            task_id ='list_dates',
            python_callable = list_dates_in_df
            )

    list_dates