public Set<BuiltInProperty> builtIns() {
        if (builtInPropertyArray == null) {
            return ImmutableSet.of();
        }
        return Arrays.stream(builtInPropertyArray).map(entry -> entry.key).collect(toImmutableSet());
    }
Returns all {@link BuiltInProperty}s in the export list.
core/src/main/java/com/linecorp/armeria/common/logging/RequestContextExporter.java