better syntax

git-svn-id: https://svn.apache.org/repos/asf/maven/maven-1/plugins/trunk@115710 13f79535-47bb-0310-9956-ffa450edef68

cruisecontrol/plugin.jelly

@@ -38,7 +38,7 @@
     </j:if>
 
     <j:set var="nagEmail" value="${pom.build.nagEmailAddress}" />
-    <j:if test="${nagEmail == ''}">
+    <j:if test="${empty(nagEmail)}">
       <ant:fail>You must specify pom.build.nagEmailAddress</ant:fail>
     </j:if>
     <j:set var="defaultSuffix" value="${maven.cruisecontrol.mail.defaultsuffix}" />