public Map<String, String> aliases() {
        if (isFrozen()) return aliases;
        if (aliases == null) return Map.of();
        return Collections.unmodifiableMap(aliases);
    }
Returns the alias to field mapping of this type as a read-only map. This is never null.
Note that all keys are lower-cased because aliases are case-insensitive
container-search/src/main/java/com/yahoo/search/query/profile/types/QueryProfileType.java