public static Headers copyOf(Headers original) {
        return new Headers(Objects.requireNonNull(original, "original"));
    }
@Test
    void copyOf() {
        Headers headers = new Headers();
        headers.set("Content-Length", "5");
        Headers headers2 = Headers.copyOf(headers);
        headers2.add("Via", "duct");

        Truth.assertThat(headers.getAll("Via")).isEmpty();
        Truth.assertThat(headers2.size()).isEqualTo(2);
        Truth.assertThat(headers2.getAll("Content-Length")).containsExactly("5");
    }