'InfluxDBClient' object has no attribute 'api_client' with Python & Docker

I'm trying to insert JSON files to influxDB database with a python script.
All my scripts are containerized via Docker.
Each time I'm trying to open the connection to insert json logs tell me that 'InfluxDBClient' object has no attribute 'api_client'

I tried a lot of different configuration, here is the actual one:

from influxdb_client import InfluxDBClient, Point, WriteOptions
from dotenv import load_dotenv
import json
import os

class DB():

    # Method to open connection
    @classmethod
    def open_con(cls):
        load_dotenv()
        cls.token = os.getenv('INFLUXDB_V2_TOKEN')
        cls.org = os.getenv('INFLUXDB_V2_ORG')
        cls.bucket = os.getenv('INFLUXDB_V2_BUCKET')
        cls.url = "http://influxdb:8086"
        cls.client = InfluxDBClient(url=cls.url, token=cls.token, org=cls.org)
        print('Connected')
        cls.write_api = cls.client.write_api(write_options=WriteOptions(batch_size=500, flush_interval=10_000, jitter_interval=2_000, retry_interval=5_000, max_retries=5, max_retry_delay=30_000, exponential_base=2))

    # Method to close connection
    @classmethod
    def close_con(cls):
        cls.client.close()

    # Method to insert JSON
    @classmethod
    def insert_json(cls, file):
        cls.open_con()
        with open(file) as f:
            file_data = json.load(f)
        cls.write_api.write(bucket=cls.bucket, org=cls.org, record=file_data)
        cls.close_con()
        print(f'Json inséré')

This is my Docker compose file:

version: "3.8"

services:
  buffer:
    image: buffer:1.0
    build:
      context: ./insert
      dockerfile: Dockerfile
    container_name: buffer
    restart: unless-stopped
    volumes:
      - ./json_files:/app/json_files
    depends_on: 
      - influxdb
  influxdb:
    image: influxdb
    container_name: influxdb
    restart: always
    ports:
      - "8086:8086"
    volumes:
      - influxdbv2:/.influxdbv2
  influxdb_cli:
    links:
      - influxdb
    image: influxdb:1.7
    container_name: influxdb_cli
    entrypoint: influx setup --bucket ${INFLUXDB_V2_BUCKET} -t ${INFLUXDB_V2_TOKEN} -o ${INFLUXDB_V2_ORG} --username=${INFLUXDB_USERNAME} --password=${INFLUXDB_PASSWORD} --host=http://influxdb:8086 -f
    restart: on-failure:10
    depends_on: 
      - influxdb
volumes:
  influxdbv2:

And finally this is the json format i'm trying to insert:

[
  {
    "measurement": "BTC @ 14/03/2021 16:52:33", 
    "tags": {
        "crypto_name": "Bitcoin", 
        "crypto_symbol": "BTC"
    }, 
    "time": "14/03/2021 16:52:33", 
    "fields": {
        "name": "Bitcoin", 
        "symbol": "BTC", 
        "currency": "$", 
        "value": 59623.19, 
        "market_cap": 1110000000000,
        "volume": 17680000000}
  }, ...
]

here is the message given by Docker logs buffer (buffer is the script that try to insert json to influxdb):

Traceback (most recent call last):
    File "./app/buffer.py", line 5, in <module>
        from influxdb_connection import DB
    File "/app/influxdb_connection.py", line 36, in <module>
        DB.open_con()
    File "/app/influxdb_connection.py", line 17, in open_con
        cls.client = InfluxDBClient(url=cls.url, token=cls.token, org=cls.org)
    File "/usr/local/lib/python3.8/site-packages/influxdb_client/client/influxdb_client.py", line 62, in __init__
    auth_header_value = "Token " + auth_token
TypeError: can only concatenate str (not "NoneType") to str
Exception ignored in: <function InfluxDBClient.__del__ at 0x7f064f97b040>
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/site-packages/influxdb_client/client/influxdb_client.py", line 171, in __del__
    if self.api_client:
AttributeError: 'InfluxDBClient' object has no attribute 'api_client'

EDIT:

I added this line to my docker compose.

...
env_file:
    - .env
...

.env is the name of my environment file.