docs: public BBContainer pollSchema() {
          BBContainer schemaCont = null;
          long segmentIndex = -1;
          if (m_memoryDeque.peek() != null) {
              StreamBlock sb = m_memoryDeque.peek();
              BBContainer cont = sb.getSchemaContainer();
              if (cont != null) {
                  return cont;
              }
              segmentIndex = sb.getSegmentIndex();
          }
          try {
              schemaCont = m_reader.getExtraHeader(segmentIndex);
          } catch (IOException e) {
              exportLog.error("Failed to poll schema: " + e);
          }
          return schemaCont;
  
      }