Inconsistency regarding exceptions

[TobiasKiecker]

I noticed a general lack of consistency regarding documentation, code and exceptions.
Particularly, I noticed two examples:

1. in AbstractRenderer
   the method setDefaultItemLabelFont(Font font, boolean notify)
   is missing a null check for the parameter font like the method setDefaultItemLabelFont(Font font) has, and the doc of both suggests.

proposed code:

    public void setDefaultItemLabelFont(Font font, boolean notify) {
        Args.nullNotPermitted(font, "font");
        this.defaultItemLabelFont = font;
        if (notify) {
            fireChangeEvent();
        }
    }

2. in CustomPieURLGenerator
   the method getURLCount(int plotIndex) needs a check of the boundaries for the provided index, similar to what getURL(Comparable<?> key, int plotIndex) has. Instead, the exception that may arise from calling_urlMaps.get(plotIndex)_ could be documented.

proposed code:

    public int getURLCount(int plotIndex) {
        int count = 0;
        if (plotIndex >= 0 && plotIndex < urlMaps.size()) {
            Map<Comparable<?>, String> map = urlMaps.get(plotIndex);
            if (map != null) {
                count = map.size();
            }
        }
        return count;
    }