@Override
                public MemberShape get(Object keyName) {
                    if ("key".equals(keyName)) {
                        return key;
                    } else if ("value".equals(keyName)) {
                        return value;
                    } else {
                        return null;
                    }
                }
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