apache/hadoop · error · IllegalArgumentException

Value of <{tagName}> is null

Error message

Value of <{tagName}> is null

What it means

ECPolicyLoader.loadSchema() reads each child field of a <schema> element and requires a non-null first text node. This IllegalArgumentException means a field element inside <schema> is empty — e.g. <k/>, <m/>, or <codec/> with no text. The message names the offending tag; k/m are reported under their internal names numDataUnits/numParityUnits.

Source

Thrown at hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/util/ECPolicyLoader.java:268

    for (int i = 0; i < fields.getLength(); i++) {
      Node fieldNode = fields.item(i);
      if (fieldNode instanceof Element) {
        Element field = (Element) fieldNode;
        String tagName = field.getTagName();
        if ("k".equals(tagName)) {
          tagName = "numDataUnits";
        } else if ("m".equals(tagName)) {
          tagName = "numParityUnits";
        }

        // Get the nonnull text value.
        Text text = (Text) field.getFirstChild();
        if (text != null) {
          String value = text.getData().trim();
          schemaOptions.put(tagName, value);
        } else {
          throw new IllegalArgumentException("Value of <" + tagName
              + "> is null");
        }
      }
    }

    return new ECSchema(schemaOptions);
  }

  /**
   * Load a EC policy from a policy element in the XML configuration file.
   * @param element EC policy element
   * @param schemas all valid schemas of the EC policy file
   * @return EC policy
   */
  private ErasureCodingPolicy loadPolicy(Element element,
                                         Map<String, ECSchema> schemas) {
    NodeList fields = element.getChildNodes();
    ECSchema schema = null;

View on GitHub (pinned to 2add963021)

Solutions

1. Give every field inside <schema> a text value: <k>6</k> <m>3</m> <codec>rs</codec>
2. Map the reported name back to the XML tag: numDataUnits=<k>, numParityUnits=<m>
3. Re-run `hdfs ec -loadPolicy` after filling in the empty element

Example fix

<!-- before -->
<schema id="rs-6-3">
  <k>6</k><m></m><codec>rs</codec>
</schema>

<!-- after -->
<schema id="rs-6-3">
  <k>6</k><m>3</m><codec>rs</codec>
</schema>

for (Element schema : schemaElements(doc)) {
  for (Node c = schema.getFirstChild(); c != null; c = c.getNextSibling()) {
    if (c instanceof Element && c.getFirstChild() == null) {
      throw new IllegalArgumentException("empty field <" + ((Element) c).getTagName() + "> in schema " + schema.getAttribute("id"));
    }
  }
}

try { new ECPolicyLoader().loadPolicy(path); }
catch (IllegalArgumentException e) {
  LOG.error("EC policy file {} rejected: {}", path, e.getMessage()); // numDataUnits=<k>, numParityUnits=<m>
}

When it happens

Trigger: `hdfs ec -loadPolicy` where a schema field is an empty element: <schema id="x"><k>6</k><m/></schema> reports 'Value of <numParityUnits> is null'.

Common situations: Deleting a field's value while editing the template, or authoring a new schema and forgetting to fill in codec or m.

Related errors

• Bad EC policy configuration file: top-level element not <con
• Bad EC policy configuration file: no <policies> element
• Bad EC policy configuration file: no <schemas> element
• Bad element in EC policy configuration file: {tagName}
• Bad policy is found in EC policy configuration file

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/120258955a93bbcc. Report an issue: GitHub.