code: public void setLogo(Component logo) {
          if (getCompositionRoot() != null && this.logo != null) {
              getCompositionRoot().removeComponent(this.logo);
          }
          this.logo = logo;
          if (logo != null) {
              logo.setPrimaryStyleName(ValoTheme.MENU_LOGO);
              logo.setSizeUndefined();
              if (getCompositionRoot() != null) {
                  getCompositionRoot().addComponentAsFirst(logo);
              }
          }
      }
docs: Adds a logo to the very top of the side bar, above the header. The logo's primary style is automatically
  set to {@link ValoTheme#MENU_LOGO} ands its size to undefined.
  
  @param logo a {@link com.vaadin.ui.Label} or {@link com.vaadin.ui.Button} to use as the logo, or {@code null} to remove the logo completely.