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

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!")