code: public void setError(@Nullable final CharSequence error, @Nullable final Drawable icon) {
          setLeftMessage(error, icon);
          setActivated(error != null);
      }
docs: Sets an error message and an icon, which should be displayed.
  
  @param error
  The error message, which should be displayed, as an instance of the type {@link
  CharSequence} or null, if a previously set error message should be cleared be
  cleared
  @param icon
  The icon, which should be displayed,as an instance of the type {@link Drawable} or
  null, if no icon should be displayed