関連ワード:  java optional ofnullable orelse    java optional.ofnullable orelsethrow    java optional ofnullable orelseget    java optional ofnullable orelse example    java optional ofnullable orelse null    java optional ofnullable map orelse    java optional ofnullable if present orelse    java 8 optional ofnullable map orelse    java optional of vs ofnullable    what is the difference between optional.of and optional.ofnullable