public boolean isMapped(String expression) {
        if (expression == null || expression.length() == 0) {
            return false;
        }
        for (int i = 0; i < expression.length(); i++) {
            char c = expression.charAt(i);
            if (c == NESTED || c == INDEXED_START) {
                return false;
            } else if (c == MAPPED_START) {
                return true;
            }
        }
        return false;
    }