equality issues and docs

src/main/java/carpet/script/value/NullValue.java

@@ -28,7 +28,7 @@ public class NullValue extends NumericValue // TODO check nonsingleton code
     public NullValue() {super(0.0D);}
 
     @Override
-    public boolean equals(final Value o)
+    public boolean equals(final Object o)
     {
         return o instanceof NullValue;
     }