public static String getScheme(SessionProtocol sessionProtocol) {
        if (sessionProtocol.isHttps()) {
            return "https";
        } else if (sessionProtocol.isHttp()) {
            return "http";
        } else {
            throw new IllegalArgumentException("sessionProtocol: " + sessionProtocol +
                                               " (expected: HTTPS, H2, H1, HTTP, H2C or H1C)");
        }
    }
Merges the given {@link RequestHeaders}. The headers have priority in the following order.
<pre>{@code
additional headers (highest priority) > headers > default headers > framework headers (lowest priority)
}</pre>
core/src/main/java/com/linecorp/armeria/internal/common/HttpHeadersUtil.java