public static String ensureAbsolutePath(String path, String paramName) {
        requireNonNull(path, paramName);
        if (path.isEmpty() || path.charAt(0) != '/') {
            throw new IllegalArgumentException(paramName + ": " + path +
                                               " (expected: an absolute path starting with '/')");
        }
        return path;
    }
Ensures that the specified {@code path} is an absolute path that starts with {@code "/"}.

@return {@code path}

@throws NullPointerException if {@code path} is {@code null}
@throws IllegalArgumentException if {@code path} is not an absolute path
core/src/main/java/com/linecorp/armeria/internal/server/RouteUtil.java