unique

import json


def get_stored_username():
    filename = 'username.json'
    try:
        with open(filename) as f:
            username = json.load(f)
    except FileNotFoundError:
        return None
    else:
        return username


def greet_user():
    username = get_stored_username()
    if username:
        print(f"Welcome back,{username}")
    else:
        username = input("What's your name")
        filename = 'username.json'
        with open(filename, 'w') as f:
            json.dump(username, f)
            print(f"We'll remember your {username}")


greet_user()

C:\Users\jin\Desktop\coder\venv\Scripts\python.exe C:\Users\jin\Desktop\coder\practice.py 
Traceback (most recent call last):
  File "C:\Users\jin\Desktop\coder\practice.py", line 29, in <module>
    greet_user()
  File "C:\Users\jin\Desktop\coder\practice.py", line 18, in greet_user
    username = get_stored_username()
  File "C:\Users\jin\Desktop\coder\practice.py", line 8, in get_stored_username
    username = json.load(f)
  File "C:\Users\jin\AppData\Local\Programs\Python\Python39\lib\json\__init__.py", line 293, in load
    return loads(fp.read(),
  File "C:\Users\jin\AppData\Local\Programs\Python\Python39\lib\json\__init__.py", line 346, in loads
    return _default_decoder.decode(s)
  File "C:\Users\jin\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\jin\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)