Set<String> getTargetImageAdditionalTags() {
    String property = getProperty(PropertyNames.TO_TAGS);
    List<String> tags =
        property != null ? ConfigurationPropertyValidator.parseListProperty(property) : to.tags;
    if (tags.stream().anyMatch(Strings::isNullOrEmpty)) {
      String source = property != null ? PropertyNames.TO_TAGS : "<to><tags>";
      throw new IllegalArgumentException(source + " has empty tag");
    }
    return new HashSet<>(tags);
  }
Gets the additional target image tags.

@return the configured extra tags.
jib-maven-plugin/src/main/java/com/google/cloud/tools/jib/maven/JibPluginConfiguration.java