Conform more of the codebase to strictNullChecks (#10358

* Conform more of the codebase to `strictNullChecks`

* Fix types

* Iterate

* Iterate

src/settings/SettingsStore.ts

@@ -511,7 +511,7 @@ export default class SettingsStore {
      * check at.
      * @return {boolean} True if the user may set the setting, false otherwise.
      */
-    public static canSetValue(settingName: string, roomId: string, level: SettingLevel): boolean {
+    public static canSetValue(settingName: string, roomId: string | null, level: SettingLevel): boolean {
         // Verify that the setting is actually a setting
         if (!SETTINGS[settingName]) {
             throw new Error("Setting '" + settingName + "' does not appear to be a setting.");