code: public Map<Integer, Date> getShards(TableDefinition tableDef) {
          checkServiceState();
          if (tableDef.isSharded()) {
              return m_shardCache.getShardMap(tableDef);
          } else {
              return new HashMap<>();
          }
      }
docs: Get all known shards for the given table. Each shard is defined in a column in the
  "_shards" row of the table's Terms store. If the given table is not sharded, an
  empty map is returned.
  
  @param tableDef  Sharded table to get current shards for.
  @return          Map of shard numbers to shard start dates. May be empty but will
  not be null.