code: public final void setPageDescriptor(PageDescriptor pageDescriptor) {
          Assert.notNull(pageDescriptor, "pageDescriptor");
          setId(pageDescriptor.getId());
          setLabel(pageDescriptor.getShowPageCommandLabel());
          setIcon(pageDescriptor.getIcon());
          setCaption(pageDescriptor.getCaption());
          this.pageDescriptor = pageDescriptor;
      }
docs: Sets the descriptor for the page that is to be opened by this command object. This
  command object will be assigned the id, label, icon, and caption from the given page
  descriptor.
  
  @param pageDescriptor The page descriptor, cannot be null.
  
  @throws IllegalArgumentException if {@code pageDescriptor} is null.