A Lookup That Might Not Find Anything, Before and After

The same lookup written twice: once returning null and once returning an Optional, with the same call site in both.

java

Customer findByReference(String ref) {
    return byRef.get(ref);
}

Customer c = findByReference(ref);
String label = c.name().toUpperCase();

line 6 throws when nothing was found, and nothing in the code suggests it might

java

Optional<Customer> findByReference(String ref) {
    return Optional.ofNullable(byRef.get(ref));
}

String label = findByReference(ref)
        .map(Customer::name)
        .map(String::toUpperCase)
        .orElse("UNKNOWN");

Optional.ofNullable wraps a value that might be null. map applies a function only when there is a value, so both map calls are skipped when the lookup found nothing, and orElse supplies the answer.

No if and no null check, and no way to reach toUpperCase on nothing. The absence is handled once, at the end, rather than at every step.