Add error checks for accessing Request members

[gspencergoog]

Description

This adds error checking and throws ArgumentError for Request subclasses which have required fields. This is because in shared.dart, in registerRequestHandler, it casts the argument's value to a Map<String, Object?>, but it doesn't do any argument checking because creating those request objects don't go through the constructors, they are just cast:

    return impl((p.value as Map?)?.cast<String, Object?>() as T);

So I added error checking to all of the accessors for required members of Request objects, so that when they are accessed they will throw.

I ran across this when a client tried to send a malformed initialization request that didn't include capabilities, and the stack trace it sent was less than helpful. This will at least send clearer errors.

Tests

• Added a test to check that these all throw. Not sure how useful that is, really, but it at least keeps them from being removed accidentally.

[github-actions]

PR Health

Changelog Entry ✔️

Package	Changed Files

Changes to files need to be accounted for in their respective changelogs.

[jakemac53]

Suggested change

	final ref = _value['ref'];
	if (ref == null) {
	throw ArgumentError('Missing ref field in $CompleteRequest.');
	}
	return ref as Reference;
	final ref = _value['ref'] as Reference?;
	if (ref == null) {
	throw ArgumentError('Missing ref field in $CompleteRequest.');
	}
	return ref;

[gspencergoog]

Fixed.

[jakemac53]

Oh actually this needs to move up into the next version 0.2.3-wip and the pubspec probably needs to be bumped as well.

[jakemac53]

LGTM once the pubspec/changelog get updated to 0.2.3-wip