simplejson.errors.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

import json
#读取
with open('tmp.json', 'r') as f:
    data = f.read()
if(not bool(data)):
    print("json is empty!")

import json
data ={"vf":"ff"}
#写入
with open('tmp.json', 'w') as f:
    json.dump(data, f)
#读取
with open('tmp.json', 'r') as f:
    data = f.read()
    print(data)
#判断
if(not bool(data)):
    print("json is empty!")