Ignore the `nulls` attribute, do not exclude null attributes on get

The `nulls` attribute is not currently being and adds noise during
validation since it's never present (and thus causes the revert message
to appear).

The `get` method excluded null or undefined values which caused issues
downstream during validation. The behavior is to merge in the current
attributes from the model in to the attributes passed for validation
which did not expose attributes that have been cleared.
Separate out _parseDate method for clarity

Remove redundant return statements
Guard against returning NaN values
Simplify names and fix logic for various cases

The `from-` and `to-` prefixes have been renamed to `upper-` and `lower-`
to be consistent with methods names.

setValue must always reset the values prior to setting new ones in
case an array-based value goes to a non-array base value (the other
value would not be cleared).

The local reference `@operator` has been removed since the order isn't
technically guarantee for the operator being set prior to the value.
Rename range scss since it applies to more than dates