code: @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);
    }
docs: Set this in the "onclick" events of links to track them
  
  @param sCategory
  The category. May not be <code>null</code>.
  @param sAction
  The action. May not be <code>null</code>.
  @param sLabel
  The label. May be <code>null</code>.
  @param aValue
  Optional numeric value. May be <code>null</code>.
  @return The JS code to be set to "onclick" event