`get_comment()`, `wp_get_post_revision()`, and `get_term()` all used to return...

`get_comment()`, `wp_get_post_revision()`, and `get_term()` all used to return by reference. Because of this, `$null` was set to `null` so the return value would be a variable where applicable. This has not been necessary since [21792], so the `$null`s have been removed.

Props toszcze.
Fixes #24768.


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