refactor: Kotlin - fix nullability

[david-allison]

This is useful before converting 'Utils.java'

Collection:

• setUserFlag
• genCards
• cardCount
• emptyCardReport
• updateFieldCache

BaseSched:

• remFromDyn

Anki2Importer:

• _writeDstMedia

How Has This Been Tested?

Unit tested

Checklist

• You have not changed whitespace unnecessarily (it makes diffs hard to read)
• You have a descriptive commit message with a short title (first line, max 50 chars).
• Your code follows the style of the project (e.g. never omit braces in if statements)
• You have commented your code, particularly in hard-to-understand areas
• You have performed a self-review of your own code
• UI changes: include screenshots of all affected screens (in particular showing any new or changed strings)
• UI Changes: You have tested your change using the Google Accessibility Scanner

[lukstbit]

@david-allison All checks are failing.

[ShridharGoel]

Seems like this was done by Android Studio, do you want to revert it?

[mikehardy]

This is apparently a really contentious area.
I read through a couple threads, and this one (with a focus around here pinterest/ktlint#48 (comment)) was informative for me.
It appears that star imports are actually a more Kotlin-y thing (IntelliJ / Android Studio add them by default, the language implementation uses them, and the package is the "unit" of import in Kotlin more than a single file like Java)

So I'm leaning towards not caring about star imports, and ktlint in it's default configuration also does not care, so I'll let this go.

Note that I'm injecting opinion here, it's a matter of taste. Feel free to disagree. If most people disagree, it's possible to configure ktlint to disallow star imports from what I understand, and that's the thing to do so these rules are enforced by tooling not convention

[mikehardy]

LGTM - long comment on star imports which I'm willing to defer to now - it either gets put into our tooling or we allow them (which would be fine by me)

Passes local re-integration