What causes "${source} has empty tag" in GoogleContainerTools/jib?

Remove empty elements from in the POM.

GoogleContainerTools/jib · error · IllegalArgumentException

${source} has empty tag

Error message

${source} has empty tag

What it means

JibPluginConfiguration.getTargetImageAdditionalTags validates the additional target-image tags (from <to><tags> or the jib.to.tags property) and throws IllegalArgumentException when any tag is null or empty. The message names the source: the property name (jib.to.tags) when set via property, otherwise '<to><tags>'.

Source

Thrown at jib-maven-plugin/src/main/java/com/google/cloud/tools/jib/maven/JibPluginConfiguration.java:478

    String property = getProperty(PropertyNames.TO_IMAGE);
    if (property != null) {
      return property;
    }
    return to.image;
  }

  /**
   * Gets the additional target image tags.
   *
   * @return the configured extra tags.
   */
  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 target image credential helper configuration.
   *
   * @return configuration for the target image credential helper
   */
  CredHelperConfiguration getTargetImageCredentialHelperConfig() {
    String property = getProperty(PropertyNames.TO_CRED_HELPER);
    if (property != null) {
      to.credHelper.setHelper(property);
    }
    return to.credHelper;
  }

  AuthConfiguration getTargetImageAuth() {

View on GitHub (pinned to fb949e2676)

Solutions

Remove empty <tag> elements from <to><tags> in the POM.
If using -Djib.to.tags, remove stray/leading/trailing commas and empty entries from the comma-separated list.
If tags come from CI variables, guard the command so empty variables are dropped, e.g. filter empty values before joining with commas.
Verify no tag is only whitespace; replace with a valid tag string.

Example fix

// before: mvn jib:build -Djib.to.tags=v1,,latest
// after: mvn jib:build -Djib.to.tags=v1,latest

Defensive patterns

Strategy: validation

Validate before calling

// Check tags before invoking Maven
String tags = String.join(",", candidateTags.stream().filter(t -> t != null && !t.isBlank()).toList());
if (candidateTags.size() != tags.split(",").length) throw new IllegalStateException("empty tag in jib.to.tags");

Prevention

Filter empty strings from CI variables before composing -Djib.to.tags.
Avoid trailing/leading commas in comma-separated tag lists.
Never commit empty <tag></tag> elements in <to><tags>.
Trim whitespace on tags when generating them from templates.

When it happens

Trigger: Setting <to><tags><tag></tag></tags> (empty tag element) or passing -Djib.to.tags=tag1,,tag3 where parseListProperty yields an empty entry between commas; trailing/leading commas in the property value also create empty entries.

Common situations: Comma-separated property lists built from CI variables where a variable is empty, hand-edited POMs with a placeholder <tag> never filled in, or list values generated with trailing separators.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

AI-assisted analysis of GoogleContainerTools/jib@fb949e2676 (2026-09-06). Data as JSON: /api/errors/c5a9458c57c2bbb5. Report an issue: GitHub.