code: public List<FileContainer> getRequiredAttachments() {
          List<FileContainer> requiredAttachments = new ArrayList<>();
          if (footerIconContainer != null) {
              requiredAttachments.add(footerIconContainer);
          }
          if (imageContainer != null) {
              requiredAttachments.add(imageContainer);
          }
          if (authorIconContainer != null) {
              requiredAttachments.add(authorIconContainer);
          }
          if (thumbnailContainer != null) {
              requiredAttachments.add(thumbnailContainer);
          }
          return requiredAttachments;
      }
docs: Gets the required attachments for this embed.
  
  @return The required attachments for this embed.