stanfordnlp/CoreNLP · error · IllegalArgumentException

Annotation field cannot be null

Error message

Annotation field cannot be null

What it means

CoreMapFunctionApplier wraps a Function that extracts a value from a CoreMap via an annotation key class. Its constructor requires a non-null annotationField; passing null makes it impossible to know which annotation key to read, so IllegalArgumentException 'Annotation field cannot be null' is thrown at construction time.

Solutions

1. Pass a valid Class annotation key, e.g. CoreAnnotations.TextAnnotation.class
2. Resolve the field from env first and verify non-null before constructing the applier
3. Fix the rule attributes so annotationField resolves instead of being null

Example fix

// before
new CoreMapFunctionApplier(env, null, func); // throws
// after
Class field = EnvLookup.lookupAnnotationKeyWithClassname(env, "text");
new CoreMapFunctionApplier(env, field, func);

if (annotationField == null) {
  annotationField = CoreAnnotations.TextAnnotation.class; // sensible default
}

Class requireAnnotationKey(Class key) {
  return key != null ? key : CoreAnnotations.TextAnnotation.class;
}

try {
  applier = new CoreMapFunctionApplier(env, annotationField, func);
} catch (IllegalArgumentException e) {
  if (e.getMessage().contains("Annotation field cannot be null")) {
    applier = new CoreMapFunctionApplier(env, CoreAnnotations.TextAnnotation.class, func);
  }
}

When it happens

Trigger: Constructing new CoreMapFunctionApplier(env, null, func) directly, or creating rules/extractors whose resultFunction setup passes a null annotation field (e.g. no annotationField resolved from env/attributes).

Common situations: Programmatic rule building where the annotation field lookup returned null (unregistered key name) and the null is then handed to the applier; misconfigured rule result.

Related errors

• Cannot match against null elements
• Must supply a target label to compute precision and recall…
• Invalid annotation key
• Unknown rule type:
• Error creating composite rule: no annotation field

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/492770818e5dc915. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/ling/tokensregex/SequenceMatchRules.java:1168

      if (this.group != 0) {
        // Save context so value evaluation can happen
        te.context = matched.toBasicSequenceMatchResult();
      }
      return te;
    }
  }


  public static class CoreMapFunctionApplier<T,O> implements Function<CoreMap, O> {

    final Env env;
    final Class annotationField;
    final Function<T,O> func;

    public CoreMapFunctionApplier(Env env, Class annotationField, Function<T,O> func) {
      this.annotationField = annotationField;
      if (annotationField == null) {
        throw new IllegalArgumentException("Annotation field cannot be null");
      }
      this.func = func;
      this.env = env;
    }

    @Override
    public O apply(CoreMap cm) {
      if (env != null) {
        env.push(Expressions.VAR_SELF, cm);
      }
      try {
        T field = (T) cm.get(annotationField);
        return func.apply(field);
      }  finally {
        if (env != null) {
          env.pop(Expressions.VAR_SELF);
        }
      }

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