Fix Javadoc warnings

Change-Id: Icf8b6b6f77ea80d3975aa975226a178145067adf
diff --git a/apps/optical-model/src/main/java/org/onosproject/net/optical/json/OchSignalCodec.java b/apps/optical-model/src/main/java/org/onosproject/net/optical/json/OchSignalCodec.java
index 0fba4fa..08d4155 100644
--- a/apps/optical-model/src/main/java/org/onosproject/net/optical/json/OchSignalCodec.java
+++ b/apps/optical-model/src/main/java/org/onosproject/net/optical/json/OchSignalCodec.java
@@ -76,6 +76,7 @@
     /**
      * Returns a JSON Object representation of this instance.
      *
+     * @param j Och signal object
      * @return JSON Object representing OchSignal
      */
     public static ObjectNode encode(OchSignal j) {