Fixed null acting as a string with matching operator (~) and split() (#662)

* Fixed null acting as a string with matching operator (~)

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

@@ -44,6 +44,11 @@ public class NullValue extends NumericValue // TODO check nonsingleton code
         return  o instanceof NullValue ? 0 : -1;
     }
 
+    @Override
+    public Value in(Value value) {
+        return Value.NULL;
+    }
+
     @Override
     public String getTypeString()
     {