Nullability Annotations to Java Classes - Helper & Manager

[ParaskP7]

Parent #18904

This issue is about adding missing nullability annotations (@Nullable & @NonNull) to as many Java-related Helper & Manager classes as possible, including fields, arguments, parameters, and return values.

FYI: As a reference, few examples of such classes are ActivityLauncher.java and AnalyticsTracker.java.

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### Tasks (`Core`)
- [ ] [WordPressApp.java](https://github.com/wordpress-mobile/WordPress-Android/blob/1b38e8c84f8e8b30626406fd0568beeffd8f7676/WordPress/src/main/java/org/wordpress/android/WordPressApp.java#L4)
- [ ] [ActivityLauncher.java](https://github.com/wordpress-mobile/WordPress-Android/blob/1b38e8c84f8e8b30626406fd0568beeffd8f7676/WordPress/src/main/java/org/wordpress/android/ui/ActivityLauncher.java#L4)
- [ ] [LocaleManager.java](https://github.com/wordpress-mobile/WordPress-Android/blob/1b38e8c84f8e8b30626406fd0568beeffd8f7676/WordPress/src/main/java/org/wordpress/android/util/LocaleManager.java#L4)

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### Tasks (`GCM`)
- [ ] [GCMMessageHandler.java](https://github.com/wordpress-mobile/WordPress-Android/blob/1b38e8c84f8e8b30626406fd0568beeffd8f7676/WordPress/src/main/java/org/wordpress/android/push/GCMMessageHandler.java#L4)
- [ ] [NativeNotificationsUtils.java](https://github.com/wordpress-mobile/WordPress-Android/blob/1b38e8c84f8e8b30626406fd0568beeffd8f7676/WordPress/src/main/java/org/wordpress/android/push/NativeNotificationsUtils.java#L4)

---

### Tasks (`Analytics`)
- [ ] [AnalyticsTrackerNosara.java](https://github.com/wordpress-mobile/WordPress-Android/blob/1b38e8c84f8e8b30626406fd0568beeffd8f7676/libs/analytics/src/main/java/org/wordpress/android/analytics/AnalyticsTrackerNosara.java#L4)
- [ ] [AnalyticsTracker.java](https://github.com/wordpress-mobile/WordPress-Android/blob/1b38e8c84f8e8b30626406fd0568beeffd8f7676/libs/analytics/src/main/java/org/wordpress/android/analytics/AnalyticsTracker.java#L4)
- [ ] [LoginAnalyticsTracker.java](https://github.com/wordpress-mobile/WordPress-Android/blob/1b38e8c84f8e8b30626406fd0568beeffd8f7676/WordPress/src/main/java/org/wordpress/android/ui/accounts/login/LoginAnalyticsTracker.java#L4)
- [ ] [AnalyticsUtils.java](https://github.com/wordpress-mobile/WordPress-Android/blob/1b38e8c84f8e8b30626406fd0568beeffd8f7676/WordPress/src/main/java/org/wordpress/android/util/analytics/AnalyticsUtils.java#L4)

---

### Tasks (`Network`)
- [ ] [GravatarApi.java](https://github.com/wordpress-mobile/WordPress-Android/blob/1b38e8c84f8e8b30626406fd0568beeffd8f7676/WordPress/src/main/java/org/wordpress/android/networking/GravatarApi.java#L4)
- [ ] [StreamingRequest.java](https://github.com/wordpress-mobile/WordPress-Android/blob/1b38e8c84f8e8b30626406fd0568beeffd8f7676/WordPress/src/main/java/org/wordpress/android/networking/StreamingRequest.java#L4)

---

### Tasks (`WebView`)
- [ ] [JetpackConnectionWebViewClient.java](https://github.com/wordpress-mobile/WordPress-Android/blob/1b38e8c84f8e8b30626406fd0568beeffd8f7676/WordPress/src/main/java/org/wordpress/android/ui/JetpackConnectionWebViewClient.java#L4)
- [ ] [URLFilteredWebViewClient.java](https://github.com/wordpress-mobile/WordPress-Android/blob/1b38e8c84f8e8b30626406fd0568beeffd8f7676/WordPress/src/main/java/org/wordpress/android/util/URLFilteredWebViewClient.java#L4)
- [ ] [WPWebViewClient.java](https://github.com/wordpress-mobile/WordPress-Android/blob/1b38e8c84f8e8b30626406fd0568beeffd8f7676/WordPress/src/main/java/org/wordpress/android/util/WPWebViewClient.java#L4)
- [ ] [WPWebChromeClientWithFileChooser.java](https://github.com/wordpress-mobile/WordPress-Android/blob/1b38e8c84f8e8b30626406fd0568beeffd8f7676/WordPress/src/main/java/org/wordpress/android/ui/WPWebChromeClientWithFileChooser.java#L4)

[peril-wordpress-mobile[bot]]

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[peril-wordpress-mobile[bot]]

	Fails
:no_entry_sign:	Please add a type label to this issue. e.g. '[Type] Enhancement'

Generated by :no_entry_sign: dangerJS