code: public void verifyShard(TableDefinition tableDef, int shardNumber) {
          assert tableDef.isSharded();
          assert shardNumber > 0;
          checkServiceState();
          m_shardCache.verifyShard(tableDef, shardNumber);
      }
docs: Get the starting date of the shard with the given number in the given sharded
  table. If the given table has not yet started the given shard, null is returned.
  
  @param tableDef      {@link TableDefinition} of a sharded table.
  @param shardNumber   Shard number (must be > 0).
  @return              Start date of the given shard or null if no objects have been
  stored in the given shard yet.