diff --git a/core/api/src/main/java/org/onosproject/net/AbstractProjectableModel.java b/core/api/src/main/java/org/onosproject/net/AbstractProjectableModel.java
index 4c66e91..9444e32 100644
--- a/core/api/src/main/java/org/onosproject/net/AbstractProjectableModel.java
+++ b/core/api/src/main/java/org/onosproject/net/AbstractProjectableModel.java
@@ -88,7 +88,7 @@
     }
 
     /**
-     * Returns the currently bound driver or null of no driver is bound.
+     * Returns the currently bound driver or null if no driver is bound.
      *
      * @return bound driver; null if none
      */
diff --git a/core/api/src/main/java/org/onosproject/net/driver/Projectable.java b/core/api/src/main/java/org/onosproject/net/driver/Projectable.java
index 9cff6b4..efd6b46 100644
--- a/core/api/src/main/java/org/onosproject/net/driver/Projectable.java
+++ b/core/api/src/main/java/org/onosproject/net/driver/Projectable.java
@@ -30,7 +30,9 @@
      *
      * @param projectionClass requested projection class
      * @param <B> type of behaviour
-     * @return projection instance or null if requested projection is not supported
+     * @return projection instance
+     * @throws IllegalStateException if a driver cannot be found
+     * @throws IllegalArgumentException if the projection is not supported
      */
     <B extends Behaviour> B as(Class<B> projectionClass);