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