stanfordnlp/CoreNLP · error · IllegalArgumentException

Unknown prior type:

Error message

Unknown prior type: 

What it means

CRFNonLinearLogConditionalObjectiveFunction.getPriorType converts a prior-name string (from flags.priorType) into the internal integer constant. If the string matches none of the recognized names (L1/L2, lasso, ridge, ae-lasso, g-lasso, sg-lasso, NONE, etc.), it throws an IllegalArgumentException naming the unrecognized value. It fails fast so an unsupported regularizer is never silently ignored.

Solutions

1. Set flags.priorType to one of the supported strings exactly as listed in the source (e.g. "L2", "L1", "lasso", "ridge", "ae-lasso", "g-lasso", "sg-lasso", "NONE").
2. Check for typos or stray whitespace in the properties file value (e.g. "l2 " with a trailing space).
3. Consult SeqClassifierFlags javadoc for the exact prior names supported by your library version.
4. If a prior you need is unsupported, implement a custom prior or fall back to L2 regularization.

Example fix

// before
properties.setProperty("priorType", "elastic-net");
// after
properties.setProperty("priorType", "L2");

java.util.Set<String> ok = new java.util.HashSet<>(java.util.Arrays.asList("l1","l2","gaussianPrior","laplacianPrior","quadraticPrior","lasso","ridge","ae-lasso","g-lasso","sg-lasso","none"));
if (!ok.contains(flags.priorType.toLowerCase().trim())) throw new IllegalArgumentException("unknown priorType: " + flags.priorType);

static boolean isValidPriorType(String s) { return s != null && java.util.Arrays.stream(new String[]{"l1","l2","gaussianprior","laplacianprior","quadraticprior","lasso","ridge","ae-lasso","g-lasso","sg-lasso","none"}).anyMatch(s.trim().toLowerCase()::equals); }

try {
  CRFNonLinearLogConditionalObjectiveFunction f = new CRFNonLinearLogConditionalObjectiveFunction(data, labels, window, classIndex, labelIndices, map, flags);
} catch (IllegalArgumentException e) {
  if (e.getMessage().startsWith("Unknown prior type")) {
    log.error("Fix flags.priorType; got: " + e.getMessage());
    flags.priorType = "L2";
  } else throw e;
}

When it happens

Trigger: Constructing the non-linear CRF objective (directly or via SeqClassifierFlags.priorType) with a priorTypeStr that is misspelled, wrong-cased beyond equalsIgnoreCase support, or entirely unsupported (e.g. "elastic-net" or a typo like "l2regularization").

Common situations: Hand-editing a training properties file and typo-ing the prior name; copying a prior value from another library (e.g. sklearn "l1") that Stanford NLP does not recognize; upgrading/downgrading versions where a prior name was removed.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• Unsupported inference type: " + flags.crfType
• Unknown inference type: " + flags.inferenceType + ". Your op
• no prior specified
• No annealing type specified
• No minimizer assigned!

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/7df75fb0f2a17f42. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/ie/crf/CRFNonLinearLogConditionalObjectiveFunction.java:95

  {
    if (priorTypeStr == null) return QUADRATIC_PRIOR;  // default
    if ("QUADRATIC".equalsIgnoreCase(priorTypeStr)) {
      return QUADRATIC_PRIOR;
    } else if ("L1".equalsIgnoreCase(priorTypeStr)) {
      return L1_PRIOR;
    } else if ("HUBER".equalsIgnoreCase(priorTypeStr)) {
      return HUBER_PRIOR;
    } else if ("QUARTIC".equalsIgnoreCase(priorTypeStr)) {
      return QUARTIC_PRIOR;
    } else if (priorTypeStr.equalsIgnoreCase("lasso") ||
               priorTypeStr.equalsIgnoreCase("ridge") ||
               priorTypeStr.equalsIgnoreCase("ae-lasso") ||
               priorTypeStr.equalsIgnoreCase("g-lasso") ||
               priorTypeStr.equalsIgnoreCase("sg-lasso") ||
               priorTypeStr.equalsIgnoreCase("NONE") ) {
      return NO_PRIOR;
    } else {
      throw new IllegalArgumentException("Unknown prior type: " + priorTypeStr);
    }
  }

  CRFNonLinearLogConditionalObjectiveFunction(int[][][][] data, int[][] labels, int window, Index<String> classIndex, List<Index<CRFLabel>> labelIndices, int[] map, SeqClassifierFlags flags, int numNodeFeatures, int numEdgeFeatures, double[][][][] featureVal) {
    this.window = window;
    this.classIndex = classIndex;
    this.numClasses = classIndex.size();
    this.labelIndices = labelIndices;
    this.data = data;
    this.featureVal = featureVal;
    this.flags = flags;
    this.map = map;
    this.labels = labels;
    this.prior = getPriorType(flags.priorType);
    this.backgroundSymbol = flags.backgroundSymbol;
    this.sigma = flags.sigma;
    this.outputLayerSize = numClasses;
    this.numHiddenUnits = flags.numHiddenUnits;

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