return (RawTile) SIRassignment.get(str.contents);
assert SIRassignment.get(str) != null || !(SIRassignment.get(str) instanceof RawTile) : "Calling getTile() on a stream that is not mapped to tile"; return (RawTile) SIRassignment.get(str);
    public RawTile getTile(FlatNode str) {        if (SIRassignment == null) {            return null;        }        return (RawTile) SIRassignment.get(str.contents);    }