@Override
            boolean isStructureMemberOptional(StructureShape container, MemberShape member, Shape target) {
                if (member.hasTrait(ClientOptionalTrait.ID) || container.hasTrait(InputTrait.ID)) {
                    return true;
                }

                return SERVER.isStructureMemberOptional(container, member, target);
            }
A client, or any other kind of non-authoritative model consumer
that must honor the {@link InputTrait} and {@link ClientOptionalTrait}.
smithy-model/src/main/java/software/amazon/smithy/model/knowledge/NullableIndex.java