python celery AttributeError: 'int' object has no attribute 'upper' error

My tasks.py

from celery import Celery

app = Celery('tasks',broker='xxxxxxxxxxx')


app.conf.timezone = 'UTC'

app.conf.beat_schedule = {
    'add-every-10-seconds': {
        'task': 'tasks.test',
        'schedule': 10.0,
        'args': 'Dedeler'
    },
}


@app.task
def test(arg):
    print(arg)

I can start my worker with this command

celery -A tasks worker -l INFO -P solo --concurrency=1 -E

but when I start beat with "celery -A tasks beat"

Traceback (most recent call last):
  File "/home/diablo/PycharmProjects/PersonalityTraitModel/PersonalityTrait/bin/celery", line 8, in <module>
    sys.exit(main())
  File "/home/diablo/PycharmProjects/PersonalityTraitModel/PersonalityTrait/lib/python3.8/site-packages/celery/__main__.py", line 15, in main
    sys.exit(_main())
  File "/home/diablo/PycharmProjects/PersonalityTraitModel/PersonalityTrait/lib/python3.8/site-packages/celery/bin/celery.py", line 213, in main
    return celery(auto_envvar_prefix="CELERY")
  File "/home/diablo/PycharmProjects/PersonalityTraitModel/PersonalityTrait/lib/python3.8/site-packages/click/core.py", line 1137, in __call__
    return self.main(*args, **kwargs)
  File "/home/diablo/PycharmProjects/PersonalityTraitModel/PersonalityTrait/lib/python3.8/site-packages/click/core.py", line 1062, in main
    rv = self.invoke(ctx)
  File "/home/diablo/PycharmProjects/PersonalityTraitModel/PersonalityTrait/lib/python3.8/site-packages/click/core.py", line 1666, in invoke
    sub_ctx = cmd.make_context(cmd_name, args, parent=ctx)
  File "/home/diablo/PycharmProjects/PersonalityTraitModel/PersonalityTrait/lib/python3.8/site-packages/click/core.py", line 923, in make_context
    self.parse_args(ctx, args)
  File "/home/diablo/PycharmProjects/PersonalityTraitModel/PersonalityTrait/lib/python3.8/site-packages/click/core.py", line 1379, in parse_args
    value, args = param.handle_parse_result(ctx, opts, args)
  File "/home/diablo/PycharmProjects/PersonalityTraitModel/PersonalityTrait/lib/python3.8/site-packages/click/core.py", line 2364, in handle_parse_result
    value = self.process_value(ctx, value)
  File "/home/diablo/PycharmProjects/PersonalityTraitModel/PersonalityTrait/lib/python3.8/site-packages/click/core.py", line 2320, in process_value
    value = self.type_cast_value(ctx, value)
  File "/home/diablo/PycharmProjects/PersonalityTraitModel/PersonalityTrait/lib/python3.8/site-packages/click/core.py", line 2307, in type_cast_value
    return convert(value)
  File "/home/diablo/PycharmProjects/PersonalityTraitModel/PersonalityTrait/lib/python3.8/site-packages/click/types.py", line 75, in __call__
    return self.convert(value, param, ctx)
  File "/home/diablo/PycharmProjects/PersonalityTraitModel/PersonalityTrait/lib/python3.8/site-packages/celery/bin/base.py", line 245, in convert
    value = value.upper()
AttributeError: 'int' object has no attribute 'upper'

I am getting this error message. What is wrong with my code ?

PS: I am using heroku celery