Datepicker empty state style

[Dum6o]

Is your feature request related to a problem? Please describe.
Datepicker <sebng-datepicker> component always has error type bottom border (is-invalid style class) when user opens new empty form. Field is not required and form group FormControl doesn't have any validators.
example:

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Describe the solution you'd like
Datepicker don't have is-invalid style class when initial value is undefined.
example: