[ONOS-2499]update accordingly for ONOS-2408's review recommendation

Change-Id: I24e7c4acbe38e4286b994c5bf50d22def945fb29
diff --git a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Assert.java b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Assert.java
index 7a2f454..92a6336 100644
--- a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Assert.java
+++ b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Assert.java
@@ -32,7 +32,7 @@
      * @param lock the lock member of assert operation
      */
     public Assert(String lock) {
-        checkNotNull(lock, "lock is not null");
+        checkNotNull(lock, "lock cannot be null");
         this.op = Operations.ASSERT.op();
         this.lock = lock;
     }
diff --git a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Comment.java b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Comment.java
index c27de6b..2853e1f 100644
--- a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Comment.java
+++ b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Comment.java
@@ -32,7 +32,7 @@
      * @param comment the comment member of comment operation
      */
     public Comment(String comment) {
-        checkNotNull(comment, "comment is not null");
+        checkNotNull(comment, "comment cannot be null");
         this.op = Operations.COMMENT.op();
         this.comment = comment;
     }
diff --git a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Commit.java b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Commit.java
index f888986..c87fb6e 100644
--- a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Commit.java
+++ b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Commit.java
@@ -32,7 +32,7 @@
      * @param durable the durable member of commit operation
      */
     public Commit(Boolean durable) {
-        checkNotNull(durable, "durable is not null");
+        checkNotNull(durable, "durable cannot be null");
         this.op = Operations.COMMIT.op();
         this.durable = durable;
     }
diff --git a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Delete.java b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Delete.java
index 2254aa0..05fa9b8 100644
--- a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Delete.java
+++ b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Delete.java
@@ -41,7 +41,7 @@
      * @param where the List of Condition entity
      */
     public Delete(TableSchema schema, List<Condition> where) {
-        checkNotNull(schema, "TableSchema is not null");
+        checkNotNull(schema, "TableSchema cannot be null");
         checkNotNull(where, "where is not null");
         this.tableSchema = schema;
         this.op = Operations.DELETE.op();
diff --git a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Insert.java b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Insert.java
index 6b46195..4186945 100644
--- a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Insert.java
+++ b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Insert.java
@@ -49,9 +49,9 @@
      * @param row Row entity
      */
     public Insert(TableSchema schema, String uuidName, Row row) {
-        checkNotNull(schema, "TableSchema is not null");
-        checkNotNull(uuidName, "uuidName is not null");
-        checkNotNull(row, "row is not null");
+        checkNotNull(schema, "TableSchema cannot be null");
+        checkNotNull(uuidName, "uuid name cannot be null");
+        checkNotNull(row, "row cannot be null");
         this.tableSchema = schema;
         this.op = Operations.INSERT.op();
         this.uuidName = uuidName;
diff --git a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Mutate.java b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Mutate.java
index fd077e2..7b5e0f7 100644
--- a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Mutate.java
+++ b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Mutate.java
@@ -45,9 +45,9 @@
      */
     public Mutate(TableSchema schema, List<Condition> where,
                   List<Mutation> mutations) {
-        checkNotNull(schema, "TableSchema is not null");
-        checkNotNull(mutations, "mutations is not null");
-        checkNotNull(where, "where is not null");
+        checkNotNull(schema, "TableSchema cannot be null");
+        checkNotNull(mutations, "mutations cannot be null");
+        checkNotNull(where, "where cannot be null");
         this.tableSchema = schema;
         this.op = Operations.MUTATE.op();
         this.where = where;
diff --git a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Select.java b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Select.java
index cb73ea7..a8571c9 100644
--- a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Select.java
+++ b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Select.java
@@ -43,9 +43,9 @@
      * @param columns the List of column name
      */
     public Select(TableSchema schema, List<Condition> where, List<String> columns) {
-        checkNotNull(schema, "TableSchema is not null");
-        checkNotNull(where, "where is not null");
-        checkNotNull(columns, "columns is not null");
+        checkNotNull(schema, "TableSchema cannot be null");
+        checkNotNull(where, "where cannot be null");
+        checkNotNull(columns, "columns cannot be null");
         this.tableSchema = schema;
         this.op = Operations.SELECT.op();
         this.where = where;
diff --git a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Update.java b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Update.java
index 61e7e6f..839e834 100644
--- a/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Update.java
+++ b/ovsdb/rfc/src/main/java/org/onosproject/ovsdb/rfc/operations/Update.java
@@ -50,9 +50,9 @@
      * @param where the List of Condition entity
      */
     public Update(TableSchema schema, Row row, List<Condition> where) {
-        checkNotNull(schema, "TableSchema is not null");
-        checkNotNull(row, "row is not null");
-        checkNotNull(where, "where is not null");
+        checkNotNull(schema, "TableSchema cannot be null");
+        checkNotNull(row, "row cannot be null");
+        checkNotNull(where, "where cannot be null");
         this.tableSchema = schema;
         this.op = Operations.UPDATE.op();
         this.row = Maps.newHashMap();