readString function
A string slot, resolved. as String? answers null for a bound value the
binding engine would have produced from a number.
Implementation
String? readString(dynamic raw, RenderContext context) {
final v = context.resolve<dynamic>(raw);
if (v == null) return null;
if (v is String) return v;
if (v is num || v is bool) return v.toString();
return null;
}