public boolean setIfAbsentAndValid(String headerName, String value) {
        Objects.requireNonNull(value, "value");
        Objects.requireNonNull(headerName, "headerName");
        if (isValid(headerName) && isValid(value)) {
            String normalName = HeaderName.normalize(headerName);
            return setIfAbsentNormal(headerName, normalName, value);
        }
        return false;
    }
@Test
    void setIfAbsentAndValid() {
        Headers headers = new Headers();
        headers.add("Via", "duct");
        headers.add("Cookie", "this=that");
        headers.add("Cookie", "frizzle=frazzle");

        headers.setIfAbsentAndValid("X-Netflix-Awesome", "true");
        headers.setIfAbsentAndValid("X-Netflix-Awesome", "True");

        Truth.assertThat(headers.getAll("X-netflix-Awesome")).containsExactly("true");
        Truth.assertThat(headers.size()).isEqualTo(4);
    }