Fix REST server side exception if array of devices is given

Fixes ONOS-6637

Change-Id: I7ec201e58f9e90a026fcdc1912b04e7398d8c2de
diff --git a/web/api/src/test/resources/org/onosproject/rest/resources/post-config.json b/web/api/src/test/resources/org/onosproject/rest/resources/post-config.json
new file mode 100644
index 0000000..5353a7d
--- /dev/null
+++ b/web/api/src/test/resources/org/onosproject/rest/resources/post-config.json
@@ -0,0 +1 @@
+{"devices":{},"links":{}}