TypeConverter sample code with possible error

[cassioseffrin]

When the database final attribute has null value the DateTimeConverter will throws an error when it's convert a null value.

So I have made a correction with try catch to avoid it. May you could update the example on README.md.

class DateTimeConverter extends TypeConverter<DateTime, int> {
  @override
  DateTime decode(int databaseValue) {
    try {
      return DateTime.fromMillisecondsSinceEpoch(databaseValue);
    } catch (e) {
      return null;
    }
  }

  @override
  int encode(DateTime value) {
    try {
      return value.millisecondsSinceEpoch;
    } catch (e) {
      return null;
    }
  }
}

[cassioseffrin]

The code above was my fix to documentation, it will be nice to update the docs to help the community. As I got no response from team I am closing it.

[vitusortner]

@cassioseffrin sorry for the late reply. Feel free to open a PR to improve the project's documentation.

[cassioseffrin]

@vitusortner I have made the PR, please check it here #442

Thks!