code: public Sequence getSequence(String sequenceKey, SequenceConfig sequenceConfig) {
          Sequence sequence = sequences.get(checkNotNull(sequenceKey));
          if (null == sequence) {
              sequence = sequenceDB().openSequence(null, 
                      sequenceDB().getEntry(sequenceKey), firstNonNull(sequenceConfig, defaultSequenceConfig()));
              sequences.put(sequenceKey, sequence);
          }
          
          return sequence;
      }
docs: Returns a {@link Sequence} instance with given configuration or {@link Berkeley#defaultSequenceConfig()} if null