fix(module:datepicker): for not nullable - on clear set to defaults

[anddrzejb]

🤔 This is a ...

• New feature
• Bug fix
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• Component style update
• Bundle size optimization
• Performance optimization
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💡 Background and solution

Due to the strongly typed nature of C#, DatePicker can get either nullable or not nullable dates. When not nullable are used, clearing the values was inputing min value for DateTime. There is not much we can do about (we can decide to take current date for example). This PR fixes the not nullable clearing scenario when defaults are set - in such case, date picker will assume defaults instead of DateTime.Min. For nullable the picker will be cleared.

☑️ Self Check before Merge

⚠️ Please check all items below before review. ⚠️

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[ElderJames]

I think it's more like a reset method..

[anddrzejb]

Yes it is. Basically I retain the original functionality TValue is nullable. But if it is not, then we cannot clear it up - it will take default, which is minimum.
Without this change, if you specify:

<RangePicker TValue="DateTime[]" DefaultValue="@(new DateTime[] { DateTime.Now.AddYear(-1), DateTime.Now })" />

you will get this result

But I think it is better to set it back to defaults if they exist. Again, this is only if TValue is not nullable and defaults exist.

[ElderJames]

What if the value is made minimum when cleared, and the input box is empty?

[anddrzejb]

I guess this could be done, but I think this might send a wrong message to anyone consuming the date picker. So in this scenario, the date picker would show empty but the values (if @bind-Value="@values"), would have DateTime.Min. To be honest I wouldn't like a surprise like that in production.

[ElderJames]

I'm not sure which is people's want.

[anddrzejb]

Ok, I understand. I made this change because this is my use case and to me seemed most logical. Please remember that ppl will still have a choice - they will be able to empty completely the fields if they decide to choose DateTime?[] type for value. My scenario is only for DateTime[] and with DefaultValue existing.

[anddrzejb]

Wow, thanks 😄 that was faster than I anticipated.