write a dummy license to avoid failure

git-svn-id: https://svn.apache.org/repos/asf/maven/maven-1/plugins/trunk@114784 13f79535-47bb-0310-9956-ffa450edef68

checkstyle/plugin.jelly

@@ -91,6 +91,8 @@
       =  Though, we recommend that you edit this License.             =
       =================================================================
         </ant:echo>
+        <j:set var="maven.checkstyle.header.file" value="${maven.build.dir}/LICENSE_DUMMY.txt" />
+        <j:file name="${maven.checkstyle.header.file}" />
       </j:if>
 
       <attainGoal name="checkstyle:run"/>