There is a better way:
<c:set var="title" value="${(empty title) ? 'Default title' : title}" />
No need for custom tag in Java nor tld. Just plain JSP EL and conditional operator.
In my opinion it is shorter and cleaner than old:
<c:if test="${empty title}" >
<c:set var="title" value="Default title" />
</c:if>
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