@Override
  public Iterator<ExpressionInfo> iterator() {
    List<ExpressionInfo> list = new ArrayList<>();
    collectPrefix(list, false);
    return list.iterator();
  }
Examples where operation is null:
- GString method name: foo."$bar"()
- Argument list (has children but no operation)
spock-core/src/main/java/org/spockframework/runtime/model/ExpressionInfo.java