If rendering a StackedBarChart with stacked bars and positive values and an upper bar's value is zero, the item label should be displayed on the top of
the lower bar, not at the base of the axis. StackedBarRenderer handels the zero value as a negative value. It is an uncommon behaviour.
To do this you only have to add in StackedbarRenderer.java at line 332 an "="
--> boolean positive = (value > 0.0);