null provider changes for karaf 4.2.1 CLI

Change-Id: Iee039332a1ff00f7957b58a8bf9c320fba974e15
diff --git a/providers/null/src/main/java/org/onosproject/provider/nil/cli/NullLinkCommand.java b/providers/null/src/main/java/org/onosproject/provider/nil/cli/NullLinkCommand.java
index 263bf5a..2a32cdf 100644
--- a/providers/null/src/main/java/org/onosproject/provider/nil/cli/NullLinkCommand.java
+++ b/providers/null/src/main/java/org/onosproject/provider/nil/cli/NullLinkCommand.java
@@ -17,8 +17,12 @@
 
 import org.apache.karaf.shell.api.action.Argument;
 import org.apache.karaf.shell.api.action.Command;
+import org.apache.karaf.shell.api.action.Completion;
 import org.apache.karaf.shell.api.action.lifecycle.Service;
 import org.onosproject.cli.AbstractShellCommand;
+import org.onosproject.cli.UpDownCompleter;
+import org.onosproject.cli.net.LinkDstCompleter;
+import org.onosproject.cli.net.LinkSrcCompleter;
 import org.onosproject.net.ConnectPoint;
 import org.onosproject.provider.nil.NullProviders;
 
@@ -35,14 +39,17 @@
 
     @Argument(index = 0, name = "one", description = "One link end-point as device/port",
             required = true, multiValued = false)
+    @Completion(LinkSrcCompleter.class)
     String one = null;
 
     @Argument(index = 1, name = "two", description = "Another link end-point as device/port",
             required = true, multiValued = false)
+    @Completion(LinkDstCompleter.class)
     String two = null;
 
     @Argument(index = 2, name = "cmd", description = "up/down",
             required = true, multiValued = false)
+    @Completion(UpDownCompleter.class)
     String cmd = null;