stanfordnlp/CoreNLP · error · java.lang.RuntimeException

Unexpected class in list while converting list to map

Error message

Unexpected class in list  while converting list to map

What it means

When converting a List trie node into a Map (to add a new branching word), addPhrase re-inserts every existing element; any element that is not a Phrase aborts with 'Unexpected class in list ... while converting list to map'.

Solutions

  1. Rebuild the phrase table using only public addPhrase/readPhrases entry points
  2. Locate and remove non-Phrase elements from list nodes before inserting longer phrases
  3. Guard population code to run single-threaded or under synchronization

Example fix

// before
treeList.add(someMap); // will break later list->map conversion
// after
Phrase p = new Phrase(wordList, text, tag, data);
table.addPhrase(...); // library decides list vs map layout
Defensive patterns

Strategy: try-catch

Validate before calling

// ensure list nodes contain only Phrase before triggering list->map conversion
if (listNodeContainsNonPhrase) rebuildTable();

Type guard

static boolean convertibleList(List<?> l) { return l.stream().allMatch(o -> o instanceof Phrase); }

Try / catch

try { table.addPhrase(wordList, text, tag, data); } catch (RuntimeException e) { if (e.getMessage().contains("converting list to map")) { rebuildPhraseTableFromSource(); } else throw e; }

Prevention

When it happens

Trigger: A list node being promoted to a map contains a non-Phrase element (e.g. the single continuation Map or a foreign object), which cannot be re-keyed under the new word.

Common situations: Same corruption sources as 416–418: direct manipulation of the internal tree, deserialization that lost types, or threaded writes without synchronization.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

AI-assisted analysis of stanfordnlp/CoreNLP@1b7edd19c4 (2026-09-10). Data as JSON: /api/errors/8dbafeecf6104963. Report an issue: GitHub.

Appendix: source

Thrown at src/edu/stanford/nlp/ling/tokensregex/PhraseTable.java:436

            throw new RuntimeException("Unexpected class in list " + obj.getClass() + " while adding word "
                    + i + "(" + word + ") in phrase " + phraseText);
          }
        }
        if (!phraseAdded && nMaps == 0) {
          // add to list
          Phrase newphrase = new Phrase(wordList, phraseText, tag, phraseData);
          lookupList.add(newphrase);
          newPhraseAdded = true;
          phraseAdded = true;
          if (lookupList.size() > MAX_LIST_SIZE) {
            // convert lookupList (should consist only of phrases) to map
            Map newMap = new HashMap<String,Object>(lookupList.size());
            for (Object obj:lookupList) {
              if (obj instanceof Phrase) {
                Phrase oldphrase = (Phrase) obj;
                addPhrase(newMap, oldphrase, i+1);
              } else  {
                throw new RuntimeException("Unexpected class in list " + obj.getClass() + " while converting list to map");
              }
            }
            tree.put(word,newMap);
          }
        }
      } else {
        throw new RuntimeException("Unexpected class in list " + node.getClass() + " while adding word "
                + i + "(" + word + ") in phrase " + phraseText);
      }
      if (phraseAdded) {
        break;
      }
    }
    if (!phraseAdded) {
      if (wordList.size() == 0) {
        log.warn(phraseText + " not added");
      } else {
        Phrase oldphrase = (Phrase) tree.get(PHRASE_END);

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