cx function
Joins CSS class names into a single space-separated string, skipping nulls and blank entries.
Replaces the ad-hoc _joinClasses helper that otherwise gets copy-pasted
across sites when composing conditional classes:
classes: cx(<String?>['card', isActive ? 'is-active' : null, size]),
Implementation
String cx(List<String?> classes) =>
classes.where((String? c) => c != null && c.trim().isNotEmpty).join(' ');