d = {"name": {"first": "One","last": "Drone"},"job": "scout","recent": {},"additional": {"place": {"zone": "1","cell": "2"}}}
new_d = {key:d[key] if d[key] != {} else "" for key in d.keys()}

[user@test ~]$ rm -rf /
rm: it is dangerous to operate recursively on '/'
rm: use --no-preserve-root to override this failsafe

# -*- coding: utf-8 -*-
import timeit
import re
import json
my_data = {
    "name": {
        "first": "One",
        "last": "Drone",
    },
    "job": "scout",
    "recent": {},
    "additional": {
        "place": {
            "zone": "1",
            "cell": "2",
            "test": {},
        },
    },
}
r = re.compile(r'\{\}', re.MULTILINE).sub
def he_simple_func1(d):
    eval(re.sub(r'\{\}', '""', str(d)))
def he_simple_func2(d):
    return json.loads(r('""', str(d)).replace("'", "\""))
def fix_my_dict(my_dict):
    for name, value in my_dict.items():
        if isinstance(value, dict) and not value:
            my_dict[name] = ""
        elif isinstance(value, dict):
            my_dict[name] = fix_my_dict(value)
    return my_dict
print(timeit.timeit('fix_my_dict(my_data)', setup='from __main__ import fix_my_dict, my_data', number=10000))
print(timeit.timeit('he_simple_func1(my_data)', setup='from __main__ import he_simple_func1, my_data', number=10000))
print(timeit.timeit('he_simple_func2(my_data)', setup='from __main__ import he_simple_func2, my_data', number=10000))

0.160768985748
0.712203979492
0.274708032608

0.837685108185
6.74191403389
2.77304005623

>>> d = {1:{2:{3:{}}}}
>>> {key:d[key] if d[key] != {} else "" for key in d.keys()}
{1: {2: {3: {}}}}
>>> d.keys()
[1]