public Builder mergeRetention(com.google.protobuf.Duration value) {
      if (retentionBuilder_ == null) {
        if (((bitField0_ & 0x00000004) != 0)
            && retention_ != null
            && retention_ != com.google.protobuf.Duration.getDefaultInstance()) {
          getRetentionBuilder().mergeFrom(value);
        } else {
          retention_ = value;
        }
      } else {
        retentionBuilder_.mergeFrom(value);
      }
      if (retention_ != null) {
        bitField0_ |= 0x00000004;
        onChanged();
      }
      return this;
    }
<pre>
Optional. How long to keep automated backups before the backups are
deleted. The value should be between 1 day and 365 days. If not specified,
the default value is 35 days.
</pre>

<code>.google.protobuf.Duration retention = 3 [(.google.api.field_behavior) = OPTIONAL];
</code>
java-valkey/proto-google-cloud-valkey-v1/src/main/java/com/google/cloud/memorystore/v1/AutomatedBackupConfig.java