This method does not seem to be covered by tests. Please add a unit-test for each of the cases checked by if statements below, i.e.
- empty response
- `null`
- response starting with `{`
- response starting with `[`
- malformed response (not JSON)

Your implementation is incomplete, as these valid JSON documents are rejected:

```java
"foo" -> String "foo"
42 -> Number 42
false -> Boolean false
```

Also `"null"` response should be converted to `JSONObject.NULL`, not a plain `null` reference.

Surely parsing of JSON is a solved problem and an existing solution like Jackson can be used instead of reinventing the wheel?