protected boolean shouldBeRendered(FacesContext facesContext, UIComponent component) {
        if (component instanceof Separator) {
            return false;
        }
        try {
            component.pushComponentToEL(facesContext, component);
            return component.isRendered();
        }
        finally {
            component.popComponentFromEL(facesContext);
        }

    }
Check whether toolbar has a render relevant component. Separators themselves will be rendered regularly but if they are the
only components there is no need to render the toolbar.
primefaces/src/main/java/org/primefaces/component/toolbar/ToolbarRenderer.java