Prevent mixin failure on null/undefined supertype properties

lib/Trait.js

@@ -735,7 +735,7 @@ function mixMethods( src, dest, vis, iname, inparent )
         // TODO: this is a kluge; we'll use proper reflection eventually,
         // but for now, this is how we determine if this is an actual method
         // vs. something that just happens to be on the visibility object
-        if ( !( src[ f ].___$$keywords$$ ) )
+        if ( !( src[ f ] && src[ f ].___$$keywords$$ ) )
         {
             continue;
         }

test/Trait/ClassExtendTest.js

@@ -167,6 +167,28 @@ require( 'common' ).testCase(
     },
 
 
+    /**
+     * This test unfortunately relies on certain implementation details;
+     * we're testing at a high level here.
+     *
+     * When determining what methods need to be proxied for a mixin, ease.js
+     * checks certain properties of the supertype.  If the value is
+     * null/undefined, then it is not an object, and cannot have any such
+     * properties.
+     */
+    'Trait mixin handles supertype null values': function()
+    {
+        // note the null value
+        var C = this.Class( { foo: null, bar: undefined } ),
+            T = this.Sut.extend( C, {} );
+
+        this.assertDoesNotThrow( function()
+        {
+            C.use( T )();
+        } );
+    },
+
+
     /**
      * This is a corollary, but is still worth testing for assurance.
      *