default String getColumnKey(UIComponent parent, int rowIndex) {
        return getColumnKey(parent, String.valueOf(rowIndex));
    }
Special {@link #getColumnKey()} method which must be used when we are inside e.g.
the DataTable "row state".

@param parent
@param rowIndex
@return
primefaces/src/main/java/org/primefaces/component/api/UIColumn.java