docs: public byte[] readVarbinary() throws IOException {
          final int len = readInt();
  
          // check for null string
          if (len == VoltType.NULL_STRING_LENGTH) {
              return null;
          }
          assert len >= 0;
  
          if (len < VoltType.NULL_STRING_LENGTH) {
              throw new IOException("Varbinary length is negative " + len);
          }
          if (len > buffer.remaining()) {
              throw new IOException("Varbinary length is bigger than total buffer " + len);
          }
  
          // now assume not null
          final byte[] retval = new byte[len];
          readFully(retval);
          return retval;
      }