Paginator.validate_number implementation has undocumented change in 4.2

[ruidc]

​https://github.com/django/django/commit/9101adc8ba66556c98f3955138d72b3492a6a60c#commitcomment-123385537

This for me at least was an undesirable behavior change from 4.1
The previous behavior should either be reinstated or the change documented.

If there is agreement on direction, happy to make the PR either way.

[Mariusz Felisiak]

In the current implementation num_pages cannot be less than 1, so this branch was unused. This looks like an issue in your custom paginator.

[ruidc]

Replying to Mariusz Felisiak:

In the current implementation num_pages cannot be less than 1, so this branch was unused. This looks like an issue in your custom paginator.

From the code in main, that doesn't seem to be the case:
`
@cached_property

def num_pages(self):

"""Return the total number of pages."""
if self.count == 0 and not self.allow_empty_first_page:

return 0

...

`
Even so, the behavior for this public function changed when a valid integer of zero is passed. Is documentation of this change not in order at least?

[Mariusz Felisiak]

Replying to ruidc:

Replying to Mariusz Felisiak:

In the current implementation num_pages cannot be less than 1, so this branch was unused. This looks like an issue in your custom paginator.

From the code in main, that doesn't seem to be the case:

    @cached_property
    def num_pages(self):
        """Return the total number of pages."""
        if self.count == 0 and not self.allow_empty_first_page:
            return 0
       ...

It's not possible when allow_empty_first_page is True.

Even so, the behavior for this public function changed when a valid integer of zero is passed.

I don't agree, this branch was unreachable.