Allowing TimeHelper::diff to default to NULL (from datetime|ago twig filter) shows 'in -1 years' result

[alister]

Issue #103 removed a test that would prove this (failing) test with an (almost) identical DateTime (compared to time()) for the |ago filter:

public function testFormatDiffDefaultToIsNull()
{
    $from = new \DatetimeImmutable(date('Y-m-d H:i:s', time()));
    $to = new \DateTime(null);
    $this->assertEquals('diff.empty', $this->formatter->formatDiff($from, $to));
    // actually returns 'diff.in.year' - or 'in -1 years' for English translation
}

In a live code scenario it would happen like this in a twig template (here, profile->updatedAt is a simple DateTime, with seconds resolution):

{# profile.updatedAt is a simple DateTime #}
<p>Updated: {{ profile.updatedAt|ago() }}</p>

But, the ago() uses the profile.updatedAt as the first parameter. and defaults to NULL as the second, from the twig filter TimeExtension::diff() (calling TimeHelper::diff()).

TimeHelper::diff(), via getDatetimeObject(), takes the null and makes it a DateTime(), defaulting to 'now' (with microseconds since PHP7.2):

return new DateTime(null);

Hence, the test above, which if you edit a profile and immediately show the updatedAt|ago() in a twig template can show 'in -1 Year' as the result.

If the default, in getDatetimeObject() was return new DateTime(null ?? '@'.time()); solves the issue, but setting it to DateTime('now') would still fail because of the tiny difference in microseconds.