code: public WebhookMessageBuilder setAvatarUrl(String avatarUrl)
      {
          this.avatarUrl = Helpers.isBlank(avatarUrl) ? null : avatarUrl;
          return this;
      }
docs: Sets the avatar url that should be used for the resulting message.
  <br>This will override the default avatar of the webhook.
  
  @param  avatarUrl
  The avatar url to use for this message
  
  @return The current WebhookMessageBuilder for chaining convenience