src/java.compiler/share/classes/javax/lang/model/type/UnknownTypeException.java

@@ -75,11 +75,11 @@
     }
 
     /**
      * Returns the additional argument.
      *
-     * @return the additional argument
+     * @return the additional argument, or {@code null} if unavailable
      */
     public Object getArgument() {
         return parameter;
     }
 }