public static void assertFieldName(
    @NotNull IonReader reader,
    @Nullable String fieldName
  ) {
    String readerFieldName = reader.getFieldName();
    assert fieldName == null || fieldName.equals(readerFieldName) :
      "Expected field name '" + fieldName + "', got `" + readerFieldName + "' ";
  }
public static void assertFieldName(
    @NotNull IonReader reader,
    @Nullable String fieldName
  )