When json_string() allocated memory is freed?

Question

This is a stack trace of calling json_string() :

1. json_string(const char *value)

2. json_stringn(value, strlen(value))

3. json_stringn_nocheck(value, len)

4. string_create(value, len, 0)

string_create then call json_strndup(value,len) to duplicate value of string.

The problem is there that I couldn't find out when this allocated memory for value is freed.