public static String post(HttpURLConnection con,
        Map<String, String> headers,
        String requestBody,
        Integer connectTimeoutMs,
        Integer readTimeoutMs)
        throws IOException, UnretryableException {
        handleInput(con, headers, requestBody, connectTimeoutMs, readTimeoutMs);
        return handleOutput(con);
    }
@Test
    public void testEmptyResponse() throws IOException {
        HttpURLConnection mockedCon = createHttpURLConnection("");
        assertThrows(IOException.class, () -> HttpAccessTokenRetriever.post(mockedCon, null, null, null, null));
    }