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);