@Override
                public Collection<MemberShape> values() {
                    List<MemberShape> result = values;
                    if (result == null) {
                        result = ListUtils.of(key, value);
                        values = result;
                    }
                    return result;
                }
Get the key member shape of the map.

@return Returns the key member shape.
smithy-model/src/main/java/software/amazon/smithy/model/shapes/MapShape.java