Fixing javadoc warnings.

Change-Id: I7b99660777bf69978bf91435a63526ccb9bf8b71
diff --git a/apps/pi-demo/common/src/main/java/org/onosproject/pi/demo/app/common/AbstractUpgradableFabricApp.java b/apps/pi-demo/common/src/main/java/org/onosproject/pi/demo/app/common/AbstractUpgradableFabricApp.java
index c290da3..bd12b13 100644
--- a/apps/pi-demo/common/src/main/java/org/onosproject/pi/demo/app/common/AbstractUpgradableFabricApp.java
+++ b/apps/pi-demo/common/src/main/java/org/onosproject/pi/demo/app/common/AbstractUpgradableFabricApp.java
@@ -481,6 +481,7 @@
      * @param did     a device id
      * @param tableId a table id
      * @return a new flow rule builder
+     * @throws FlowRuleGeneratorException if device has no pipeline interpreter
      */
     protected FlowRule.Builder flowRuleBuilder(DeviceId did, PiTableId tableId)
             throws FlowRuleGeneratorException {