static <T> ResponseEntity<T> of(ResponseHeaders headers, T content, HttpHeaders trailers) {
        requireNonNull(headers, "headers");
        requireNonNull(content, "content");
        requireNonNull(trailers, "trailers");
        return new DefaultResponseEntity<>(headers, content, trailers);
    }
Returns a newly created {@link ResponseEntity} with the specified {@link ResponseHeaders},
{@code content} and {@linkplain HttpHeaders trailers}.
core/src/main/java/com/linecorp/armeria/common/ResponseEntity.java