Помогите разобраться с проблемой json, не могу понять что за ошибка

import json

filename = 'username.json'
try:
    with open(filename) as f_obj:
        username = json.load(f_obj)
except FileNotFoundError:
    username = input("What's you name? ")
    with open(filename, 'w') as f_obj:
        json.dump(username, f_obj)
        print("We'll remember you when you come back, " + username + "!")
else:
    print("Welcome back, " + username + "!")

В коммандной строке следующее:

C:\Python>New.py
Traceback (most recent call last):
  File "C:\Python\New.py", line 6, in <module>
    username = json.load(f_obj)
  File "C:\Users\999\AppData\Local\Programs\Python\Python39\lib\json\__init__.py", line 293, in load
    return loads(fp.read(),
  File "C:\Users\999\AppData\Local\Programs\Python\Python39\lib\json\__init__.py", line 346, in loads
    return _default_decoder.decode(s)
  File "C:\Users\999\AppData\Local\Programs\Python\Python39\lib\json\decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "C:\Users\999\AppData\Local\Programs\Python\Python39\lib\json\decoder.py", line 355, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)