getValueAt(index) {
    const date = this.date || this.emptyValue;
    if (date) {
      this.refs.input[index].value = date;
      return this.refs.input[index].value;
    }
    else {
      this.refs.input[index].value = '';
      return null;
    }
  }
Get the value at a specific index.
@param {number} index - The index to get the value from.
@returns {*} - The value at index.