@java.lang.Override
        public Builder toBuilder() {
            return this == DEFAULT_INSTANCE
                    ? new Builder()
                    : new Builder().mergeFrom(this);
        }
<code>optional string format = 4;</code>

@return The bytes for format.
turms-server-common/src/main/java/im/turms/server/common/access/client/dto/model/file/AudioFile.java