stanfordnlp/CoreNLP · error · IllegalArgumentException

Unknown property: " + names.iterator().next()

Error message

Unknown property: " + names.iterator().next()

What it means

PropertiesUtils.checkProperties(properties, defaults) verifies that every key in 'properties' is present in the 'defaults' property set, catching typos in configuration files. Unknown keys throw IllegalArgumentException, with a singular message when exactly one unknown key remains and a plural message otherwise.

Solutions

1. Correct the property name to match a known key in defaults (check spelling)
2. Compare against the documentation or the defaults Properties object for valid key names
3. Remove the obsolete/unknown key if it is no longer supported in this CoreNLP version
4. Prefix component-specific options correctly (e.g. 'customAnnotator.myAnnotator.x' for custom annotators)

Example fix

// before
props.setProperty("annotater", "tokenize,ssplit"); // typo
// after
props.setProperty("annotators", "tokenize,ssplit");

Set<String> known = defaults.stringPropertyNames();
List<String> unknown = properties.stringPropertyNames().stream()
    .filter(k -> !known.contains(k)).collect(Collectors.toList());
if (!unknown.isEmpty()) System.err.println("Unknown property keys: " + unknown);

try {
  PropertiesUtils.checkProperties(userProps, defaultProps);
} catch (IllegalArgumentException e) {
  logger.warning("Config check failed: " + e.getMessage() + " — ignoring and continuing with defaults");
  // or fail fast, depending on strictness
}

When it happens

Trigger: Calling checkProperties(userProps, defaultsProps) where userProps contains at least one key not present in defaults' stringPropertyNames — typically after removing known defaults leaves a nonempty remainder.

Common situations: Typo in a CoreNLP properties file (e.g. 'annotator' instead of 'annotators'); using a property name from an older CoreNLP version that has since been renamed; passing pipeline options as top-level keys without the required prefix.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

• Unknown properties: " + names
• annotator " " requires annotation " ". The usual…
• Both parse.model and parse.executable properties must be…
• Cannot determine annotation key for
• Cannot have these two ordering constraints

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/f60d0a47bcaaa67d. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/util/PropertiesUtils.java:142

  /**
   * Checks to make sure that all properties specified in {@code properties}
   * are known to the program by checking that each simply overrides
   * a default value.
   *
   * @param properties Current properties
   * @param defaults Default properties which lists all known keys
   */
  @SuppressWarnings("unchecked")
  public static void checkProperties(Properties properties, Properties defaults) {
    Set<String> names = Generics.newHashSet();
    names.addAll(properties.stringPropertyNames());
    for (String defaultName : defaults.stringPropertyNames()) {
      names.remove(defaultName);
    }
    if ( ! names.isEmpty()) {
      if (names.size() == 1) {
        throw new IllegalArgumentException("Unknown property: " + names.iterator().next());
      } else {
        throw new IllegalArgumentException("Unknown properties: " + names);
      }
    }
  }

  /**
   * Build a {@code Properties} object containing key-value pairs from
   * the given data where the keys are prefixed with the given
   * {@code prefix}. The keys in the returned object will be stripped
   * of their common prefix.
   *
   * @param properties Key-value data from which to extract pairs
   * @param prefix Key-value pairs where the key has this prefix will
   *               be retained in the returned {@code Properties} object
   * @return A Properties object containing those key-value pairs from
   *         {@code properties} where the key was prefixed by
   *         {@code prefix}. This prefix is removed from all keys in

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