SettingsBase: Allow null as defaultValue

​Maintenance

Affected app variants: all

Summary

The SettingsBase<T> interface (and by extension SettingsEntry<T>) should allow null as the defaultValue in addition to T.

SettingsBase<T> and SettingsEntry<T> should have unknown as the default for the type variable.

Background

This helps resolve the following eslint error: "Object literal's property 'defaultValue' implicitly has an 'any' type."

const settingsEntry =	{
		// ...
		defaultValue:	null, // error :(
}

⬇

const settingsEntry: SettingsEntry<unknown> =	{
		// ...
		defaultValue:	null, // no error :)
}

Acceptance Criteria

• SettingsBase<T> interface allows null as the defaultValue in addition to T.
• SettingsBase<T> and SettingsEntry<T> specify unknown as the default for the type variable.
• The linting error is resolved.