Since we have the ability to use `not` as a prefix, having rules that
validate negative behaviour makes them a bit inflexible, verbose, and
harder to understand.
This commit will refactor the `NotEmpty`, and rename it to `Falsy`. It
will no longer trim strings, because Blank does a much better job at it;
it only simulates the behaviour of PHP’s native `empty()` function.
Because `Falsy`, `Blank`, and `Undef` have similar behaviour, I created
a page to demonstrate the difference and show when the user should use
one or the other.
Assisted-by: Cursor (claude-4.5-opus-high)
