stanfordnlp/CoreNLP · error · IllegalArgumentException

fromValues() must take an array with 2 elements

Error message

fromValues() must take an array with 2 elements

What it means

Span.fromValues(Object... values) accepts either exactly one value (creating a one-token span) or exactly two values (start, end). Any other arity throws this IllegalArgumentException because a span cannot be defined from 0 or 3+ values.

Solutions

1. Call fromValues with exactly one or two arguments; fix the call site arity.
2. If you have 3+ values, extract only the start/end pair you need.
3. For one-token spans pass a single value (the library computes end = value + 1).
4. Add a caller-side length check on the values array before invoking.

Example fix

// before
Span s = Span.fromValues(start, end, label);
// after
Span s = Span.fromValues(start, end);

if (values == null || (values.length != 1 && values.length != 2)) {
  throw new IllegalArgumentException("Span.fromValues requires 1 or 2 values, got " + (values == null ? 0 : values.length));
}

try { Span s = Span.fromValues(vals); } catch (IllegalArgumentException e) { /* fix arity at call site */ }

When it happens

Trigger: Calling Span.fromValues() with an empty varargs array, or accidentally passing 3+ arguments (e.g. start, end, plus an extra label), or spreading an array/list of wrong length.

Common situations: Refactoring code that changed span arity, passing a token list directly to fromValues, generic code that forwards a values array of arbitrary length.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• Unknown value for span
• Not sure if RVFDataset runs correctly in this method…
• minValue for feature
• maxValue for feature
• datum

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/4681a42305efbef9. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/ie/machinereading/structure/Span.java:62

  }
  
  /**
   * Safe way to construct Spans if you're not sure which value is higher.
   */
  @SuppressWarnings("UnusedDeclaration")
  public static Span fromValues(int val1, int val2) {
    if (val1 <= val2) {
      return new Span(val1, val2);
    } else {
      return new Span(val2, val1);
    }
  }

  public static Span fromValues(Object... values) {
    if (values.length == 1) {
      return fromValues(values[0], values[0] instanceof Number ? ((Number) values[0]).intValue() + 1 : Integer.parseInt(values[0].toString()) + 1);
    }
    if (values.length != 2) { throw new IllegalArgumentException("fromValues() must take an array with 2 elements"); }
    int val1;
    if (values[0] instanceof Number) { val1 = ((Number) values[0]).intValue(); }
    else if (values[0] instanceof String) { val1 = Integer.parseInt((String) values[0]); }
    else { throw new IllegalArgumentException("Unknown value for span: " + values[0]); }
    int val2;
    if (values[1] instanceof Number) { val2 = ((Number) values[1]).intValue(); }
    else if (values[0] instanceof String) { val2 = Integer.parseInt((String) values[1]); }
    else { throw new IllegalArgumentException("Unknown value for span: " + values[1]); }
    return fromValues(val1, val2);
  }

  public int start() { return start; }
  public int end() { return end; }
  
  public void setStart(int s) { start = s; }
  public void setEnd(int e) { end = e; }
  
  @Override

View on GitHub (pinned to 1b7edd19c4)