refactored Matrix generation code into a tag.

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@3546 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/Functions.java

@@ -34,6 +34,8 @@ import java.util.List;
 import java.util.Map;
 import java.util.SortedMap;
 import java.util.TreeMap;
+import java.util.Collection;
+import java.util.Collections;
 import java.util.logging.LogRecord;
 import java.util.logging.SimpleFormatter;
 import java.lang.management.ManagementFactory;
@@ -514,4 +516,8 @@ public class Functions {
        sb.append('\n');
        return sb.toString();
     }
+
+    public static <T> Collection<T> emptyList() {
+        return Collections.emptyList();
+    }
 }