docs: @Nonnull
    public static JSInvocation createEventTrackingCode (@Nonnull final String sCategory,
                                                        @Nonnull final String sAction,
                                                        @Nullable final String sLabel,
                                                        @Nullable final Integer aValue)
    {
      final JSArray aArray = new JSArray ().add ("_trackEvent").add (sCategory).add (sAction);
      if (StringHelper.hasText (sLabel))
        aArray.add (sLabel);
      if (aValue != null)
        aArray.add (aValue.intValue ());
  
      return JSExpr.ref ("_gaq").invoke ("push").arg (aArray);
    }