accessing session in gsp throws 'Cannot create a session after the response has been committed' error?

Question

In the base layout, i have the following code to show the cart count.

<g:if test="${session['products-ids']}">

    <g:link elementId="cart-link" controller="payment" action="productsPurchaseSummary">
        <div id="cart-image">
            <span id="cart-count">
                <%
                    println session['products-ids'].split(",").size()
                %>
            </span>
        </div>
    </g:link>

</g:if>

This code is throwing error at the point when session['products-ids'] is checked. The error is as follows:

Caused by: java.lang.IllegalStateException: Cannot create a session after the response has been committed
    at C__Users_Lenovo_IdeaProjects_grails_app_views_layouts__cart_gsp.run(C__Users_Lenovo_IdeaProjects_grails_app_views_layouts__cart_gsp:19)
    ... 5 more

When i donot access the session then the view renders. So i wonder whether there is a way to access session in view safely. I am using Grails 2.2. Thanks for the help!