code: public com.google.api.ads.adwords.axis.v201809.cm.Image getHeaderImage() {
          return headerImage;
      }
docs: Gets the headerImage value for this GmailAd.
  
  @return headerImage   * Header image. An image must first be created using the MediaService,
  and Image.mediaId must be
  populated when creating a {@link "GmailAd"}. Valid
  image types are GIF, JPEG, and PNG. The
  minimum size is 300x100 and the aspect ratio must
  be in 3:1 to 5:1 (+-1%).
  <span class="constraint Selectable">This field
  can be selected using the value "GmailHeaderImage".</span>