empty is an operator:
empty
The empty operator is a prefix operation that can be used to determine whether a value is null or empty.
<c:if test="${empty myObject.featuresList}">
There's also the function tags, a bit more flexible:
<%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %><c:if test="${fn:length(list) > 0}">
And here's the tag documentation.