[EventDispatcher] don't count empty listeners

When event listeners for certain events are removed from the event
dispatcher, empty arrays are not being removed. Therefore, counting
on empty arrays leads to wrong results of the hasListeners() method.
Unify null comparisons
remove unused imports
minor #11481 Unify null comparisons (WouterJ)

This PR was merged into the 2.3 branch.

Discussion
----------

Unify null comparisons

| Q             | A
| ------------- | ---
| Fixed tickets | -
| License       | MIT

Commits
-------

be04c50 Unify null comparisons
fixed CS
minor #11484 remove unused imports (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
----------

remove unused imports

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

Commits
-------

9cd059e remove unused imports
bug #11475 [EventDispatcher] don't count empty listeners (xabbuh)

This PR was merged into the 2.3 branch.

Discussion
----------

[EventDispatcher] don't count empty listeners

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11444
| License       | MIT
| Doc PR        |

When event listeners for certain events are removed from the event
dispatcher, empty arrays are not being removed. Therefore, counting
on empty arrays leads to wrong results of the hasListeners() method.

Thanks to @mlindenb for discovering this an proposing a solution.

Commits
-------

fdbb04a [EventDispatcher] don't count empty listeners
Update validators.eu.xlf

Spelling of 'CSRF' was incorrect
minor #11491 Update validators.eu.xlf (g123456789l)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #11491).

Discussion
----------

Update validators.eu.xlf

Spelling of 'CSRF' was incorrect

Commits
-------

d432395 Update validators.eu.xlf