static BodyPart of(HttpHeaders headers, CharSequence content) {
        requireNonNull(content, "content");
        return of(headers, HttpData.ofUtf8(content));
    }
Returns a new UTF-8-encoded {@link BodyPart} using the specified {@link HttpHeaders} and
{@link CharSequence}.
core/src/main/java/com/linecorp/armeria/common/multipart/BodyPart.java