:Revise behaviour to return empty list

Change-Id: I5e1dfa80cab1b8a8c5a245421be38b44e629cab3
diff --git a/core/api/src/test/java/org/onosproject/net/driver/DefaultDriverTest.java b/core/api/src/test/java/org/onosproject/net/driver/DefaultDriverTest.java
index 330ec8b..2062951 100644
--- a/core/api/src/test/java/org/onosproject/net/driver/DefaultDriverTest.java
+++ b/core/api/src/test/java/org/onosproject/net/driver/DefaultDriverTest.java
@@ -41,6 +41,7 @@
                                               ImmutableMap.of("foo", "bar"));
         assertEquals("incorrect name", "foo.bar", ddc.name());
         assertEquals("incorrect parent", ddp, ddc.parent());
+        assertEquals("incorrect empty parent", ImmutableList.of(), ddp.parents());
         assertEquals("incorrect mfr", "Circus", ddc.manufacturer());
         assertEquals("incorrect hw", "lux", ddc.hwVersion());
         assertEquals("incorrect sw", "1.2a", ddc.swVersion());