private com.google.protobuf.MapField<java.lang.String, java.lang.String>
      internalGetCustomMetadata() {
    if (customMetadata_ == null) {
      return com.google.protobuf.MapField.emptyMapField(
          CustomMetadataDefaultEntryHolder.defaultEntry);
    }
    return customMetadata_;
  }
<pre>
Optional. Updates objects Custom-Time fixed metadata. Unset values will be
ignored. Set empty values to clear the metadata. Refer to documentation in
https://cloud.google.com/storage/docs/metadata#custom-time.
</pre>

<code>optional string custom_time = 6 [(.google.api.field_behavior) = OPTIONAL];</code>

@return The bytes for customTime.
java-storagebatchoperations/proto-google-cloud-storagebatchoperations-v1/src/main/java/com/google/cloud/storagebatchoperations/v1/PutMetadata.java