message: DiffArray::label_ was broken
diff: @@ -1647,13 +1647,16 @@ struct DiffArray : ArrayBase<value_t<Type_>, is_mask_v<Type_>, DiffArray<Type_>>
  }
  const char *label_() const {
  + const char *result = nullptr;
  if constexpr (IsEnabled) {
  if (m_index > 0)
  - detail::ad_label<Type>(m_index);
  + result = detail::ad_label<Type>(m_index);
  }
  - if constexpr (is_jit_array_v<Type>)
  - return m_value.label_();
  - return nullptr;
  + if constexpr (is_jit_array_v<Type>) {
  + if (!result)
  + result = m_value.label_();
  + }
  + return result;
  }
  static const char *graphviz_() {
  