Recursive method causing memory leak

Question

I was stumbled upon finding this function leaking after running tracemalloc on my application;

By running tracemalloc.take_snapshot().statistics('traceback'), within the first line I could find a traceback leading to this function:

def sanitize_nested_object(value):
    # Remove unicode character that can not be save to database as text
    invalid_unicode = '\x00'

    if type(value) == dict:
        return {
            sanitize_nested_object(k): sanitize_nested_object(v) # <-- This line
            for k, v in value.items()
        }
    if type(value) == list:
        return [sanitize_nested_object(el) for el in value]
    if type(value) == str:
        return value.replace(invalid_unicode, '')
    return value

With trace statistics of size=5050992 and count=678 it seems traceback.format() points to this particular line: sanitize_nested_object(k): sanitize_nested_object(v).

I am actually unsure on how to pursue investigating, and I'm thinking of wether the leak comes from the recursion, the in-line dictionary, or array generation.

What could be some next steps to debug the leak, and if this function is actually leaking, what could make it do so?