throw new XRRuntimeException("Could not find sibling to: " + which);
return null;
    public Content getNextInFlowSibling(LayoutContext c, Content which) {        for (Iterator i = getChildContent(c).iterator(); i.hasNext();) {            Object obj = i.next();            if (obj == which) {                while (i.hasNext()) {                    Object result = i.next();                    if (ContentUtil.isNotInFlow(result)) {                        continue;                    }                    return (Content) result;                }                return null;            }        }        throw new XRRuntimeException("Could not find sibling to: " + which);    }