JetBrains/intellij-community · error · NullPointerException

Access by hierarchical idx %s failed: Encountered an unexpec

Error message

Access by hierarchical idx %s failed: Encountered an unexpected nested collection by path %s. Only arrays or lists are allowed as nested collections

What it means

extractValueByHierarchicalIndex accepts Object[] and List as nested collections but throws (as NullPointerException) when a path level resolves to some other Collection type (e.g. Set, Queue, Collection from a stream). The message states that only arrays or lists are allowed as nested collections.

Source

Thrown at grid/core-impl/src/datagrid/HierarchicalColumnsDataGridModel.java:465

            "Access by hierarchical idx %s failed: Encountered a null element by path %s.",
            Arrays.toString(hierarchicalIdx),
            Arrays.toString(Arrays.copyOfRange(hierarchicalIdx, 0, i))
          )
        );
      }

      if (result instanceof Object[] vals) {
        data = vals;
        continue;
      }

      if (result instanceof List<?> vals) {
        data = vals.toArray();
        continue;
      }

      if (result instanceof Collection) {
        throw new NullPointerException(
          String.format(
            "Access by hierarchical idx %s failed: Encountered an unexpected nested collection by path %s. Only arrays or lists are allowed as nested collections",
            Arrays.toString(hierarchicalIdx),
            Arrays.toString(Arrays.copyOfRange(hierarchicalIdx, 0, i))
          )
        );
      }

      break;
    }

    return result;
  }

  private static int[] addIntToArray(int[] array, int value) {
    int[] newArray = new int[array.length + 1];
    System.arraycopy(array, 0, newArray, 0, array.length);
    newArray[array.length] = value;

View on GitHub (pinned to be881553f2)

Solutions

1. Convert nested collections to List or Object[] when building row values (e.g. new ArrayList<>(set) or set.toArray()).
2. Add an ingestion-time check rejecting/wrapping non-list Collections.
3. If ordering is irrelevant, sort deterministically before converting to keep paths stable.

Example fix

// before
values[0] = someSet; // Set at nested level

// after
values[0] = new ArrayList<>(someSet); // List is supported

Object v = values[level];
if (v instanceof Collection c && !(v instanceof List)) {
  v = new ArrayList<>(c); // normalize to supported List
  values[level] = v;
}

static boolean isSupportedNestedValue(Object o) {
  return o == null || o instanceof Object[] || o instanceof List || !(o instanceof Collection);
}

When it happens

Trigger: Row values containing a Set/HashSet or other non-list Collection at a level the hierarchical path traverses; converting JSON/DB data where a nested field was materialized as a Set.

Common situations: Data ingestion code that stores arbitrary Java collections into row values; version changes where a producer switched from List to Set for nested elements.

Related errors

• Row %d failed: hierarchicalIdx cannot be null
• Row %d access failed: hierarchicalIdx cannot be empty
• Row %d access failed: %s
• Access by hierarchical idx %s failed: Index out of bounds at
• Access by hierarchical idx %s failed: Encountered a null ele

AI-assisted analysis of JetBrains/intellij-community@be881553f2 (2026-08-14). Data as JSON: /api/errors/991d8f6d3668847e. Report an issue: GitHub.