Merge pull request #948 from fanf/bug_7360/exception_exception_caught…

…_during_polcy_update_process_empty_max

Fixes #7360: Exception: Exception caught during polcy update process: empty.max

rudder-core/src/main/scala/com/normation/rudder/services/policies/write/PrepareTemplateVariables.scala

@@ -286,7 +286,7 @@ class PrepareTemplateVariablesImpl(
 
     //utilitary method for formating list of "promisee usebundle => bundlename;"
     def formatUsebundle(x:Seq[(Technique, String, Bundle)]) = {
-      val alignWidth = x.map(_._2.size).max
+      val alignWidth = if(x.size <= 0) 0 else x.map(_._2.size).max
       x.map { case (t, promiser, bundle) => s""""${promiser}"${" "*Math.max(0, alignWidth - promiser.size)} usebundle => ${bundle.name};"""}.mkString( "\n")
     }