stanfordnlp/CoreNLP · error · IllegalArgumentException

Null index array

Error message

Null index array

What it means

Alignment.makeFromIndexArray throws IllegalArgumentException when the supplied int[] of node indexes is null. The method aligns nodes of a hypothesis Semgraph to a text Semgraph and requires an index array exactly matching the hypothesis graph's size, so a null array cannot be processed.

Solutions

1. Ensure the int[] passed as indexes is allocated and populated before calling makeFromIndexArray
2. Add a null check on the caller side and return an empty Alignment or throw a descriptive error upstream
3. Verify the upstream method producing the index array never returns null on failure paths

Example fix

// before
Alignment align = Alignment.makeFromIndexArray(txtGraph, hypGraph, null, justification);
// after
if (indexes == null) { throw new IllegalStateException("No alignment indexes computed"); }
Alignment align = Alignment.makeFromIndexArray(txtGraph, hypGraph, indexes, justification);

if (indexes == null) throw new IllegalArgumentException("indexes must be non-null");
if (hypGraph != null && indexes.length != hypGraph.size()) throw new IllegalArgumentException("indexes length mismatch");

boolean isValidIndexes(int[] indexes, SemGraph hypGraph) { return indexes != null && hypGraph != null && indexes.length == hypGraph.size(); }

try { Alignment a = Alignment.makeFromIndexArray(txtGraph, hypGraph, indexes, j); } catch (IllegalArgumentException e) { log.error("Bad alignment input: " + e.getMessage()); }

When it happens

Trigger: Calling Alignment.makeFromIndexArray(txtGraph, hypGraph, null, ...) with a null int[] indexes argument, typically when the alignment array comes from an upstream computation that returned null.

Common situations: Pipeline code where alignment indexes are produced by another method (e.g. a matcher or aligner) that can return null on no match; uninitialized array fields passed straight into the factory method.

Related errors

• Must supply a target label to compute precision and recall…
• Annotation field cannot be null
• Cannot match against null elements
• Invalid txtGraph
• Invalid hypGraph

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/371f6155a807605a. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/semgraph/semgrex/Alignment.java:164

  /**
   * Constructs and returns a new Alignment from the given hypothesis
   * {@code SemanticGraph} to the given text (passage) SemanticGraph, using
   * the given array of indexes.  The i'th node of the array should contain the
   * index of the node in the text (passage) SemanticGraph to which the i'th
   * node in the hypothesis SemanticGraph is aligned, or -1 if it is aligned to
   * NO_WORD.
   */
  public static Alignment makeFromIndexArray(SemanticGraph txtGraph,
                                             SemanticGraph hypGraph,
                                             int[] indexes,
                                             double score,
                                             String justification) {
    if (txtGraph == null || txtGraph.isEmpty())
      throw new IllegalArgumentException("Invalid txtGraph " + txtGraph);
    if (hypGraph == null || hypGraph.isEmpty())
      throw new IllegalArgumentException("Invalid hypGraph " + hypGraph);
    if (indexes == null)
      throw new IllegalArgumentException("Null index array");
    if (indexes.length != hypGraph.size())
      throw new IllegalArgumentException("Index array length " + indexes.length +
                                         " does not match hypGraph size " + hypGraph.size());
    Map<IndexedWord, IndexedWord> map =
      Generics.newHashMap();
    for (int i = 0; i < indexes.length; i++) {
      IndexedWord hypNode = hypGraph.getNodeByIndex(i);
      IndexedWord txtNode = IndexedWord.NO_WORD;
      if (indexes[i] >= 0)
        txtNode = txtGraph.getNodeByIndex(indexes[i]);
      map.put(hypNode, txtNode);
    }
    return new Alignment(map, score, justification);
  }

  public static Alignment makeFromIndexArray(SemanticGraph txtGraph,
                                             SemanticGraph hypGraph,
                                             int[] indexes) {

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