How to get an item from itemId in a Table's style generator?

In a Table, I want to set a cell's style based on another cell's contents.

So I have a cell style generator working. The problem is the "getStyle" method is passed only an itemId and a propertyId. I need access to another property on the same item.

--> How do I get to an Item instance from only the itemId?

So in this example, I want the FirstName cell to have color if that person is a boss ("IsBoss" property).

// style generator
        // The returned style name will be concatenated to prefix "v-table-cell-content-".
        table.setCellStyleGenerator(new Table.CellStyleGenerator() {
            public String getStyle(Object itemId, Object propertyId) {
                if (propertyId == null) {
                    // no propertyId, styling row
                    return null;
                } else if ("FirstName".equals(propertyId)) {
// How do I get the item?
// I need a sibling property on the same item.
                    if ( item.getItemProperty( "IsBoss" ).getValue() ) == true ) {
                      return "is_boss";
                    } else {
                      return null;
                    }
                } else {
                    // no style
                    return null;
                }

            }

        });