Step 1 - Conditional access ?.

void main() {
  String? s = null;
  print(s?.length);
  s = 'hi';
  print(s?.length);
}

• If the receiver is null, the whole expression short-circuits to null (unless context requires promotion elsewhere).

Step 2 - Coalesce ??

void main() {
  String? a = null;
  String b = a ?? 'fallback';
  print(b);
}

• ?? picks the right side only when the left is null.

Step 3 - Assign if null ??=

void main() {
  String? cache;
  cache ??= 'loaded';
  cache ??= 'ignored';
  print(cache);
}

Step 4 - Why avoid !

• value! tells the compiler “trust me, not null.” A wrong ! throws at runtime.
• Replace with checks, early returns, ??, or refactor APIs to return non-null when possible.

Practice tasks

• Rewrite String x = maybe!; using if (maybe != null) { ... } with a local variable.
• Chain user?.profile?.avatarUrl ?? 'default.png' with nullable user and profile.
• Use ??= to lazily initialize a List<String>? buffer once.