Fixed little error introduced during previous commits. Only display a "Fixes [...]" text if there's an issue attribute defined.

git-svn-id: https://svn.apache.org/repos/asf/maven/maven-1/plugins/trunk@114344 13f79535-47bb-0310-9956-ffa450edef68

changes/src/plugin-resources/changes.jsl

@@ -56,7 +56,7 @@
         <td><img src="images/${type}.gif" alt="${type}"/></td>
         <td>
           <jsl:applyTemplates trim="false"/>
-          <j:if test="${issue != null}">
+          <j:if test="${issue != ''}">
             <j:useBean var="finder" class="org.apache.maven.changes.IssueFinder"/>
             <j:set var="template" value="${maven.changes.issue.template}"/>
             <j:set var="trackerURL" value="${pom.issueTrackingUrl}"/>