public void setFooterBuilder(FooterBuilder<T> builder) {
        assert builder != null : "builder cannot be null";
        this.footerBuilder = builder;
        redrawFooters();
    }
Set the {@link HeaderBuilder} used to build the footer section of the
table.
stroom-core-client-widget/src/main/java/com/google/gwt/user/cellview/client/AbstractCellTable.java