code: private void readSessions(CoronaSerializer coronaSerializer)
      throws IOException {
      coronaSerializer.readField("sessions");
      // Expecting the START_OBJECT token for sessions
      coronaSerializer.readStartObjectToken("sessions");
      JsonToken current = coronaSerializer.nextToken();
      while (current != JsonToken.END_OBJECT) {
        String sessionId = coronaSerializer.getFieldName();
        Session session = new Session(clusterManager.conf.getCMHeartbeatDelayMax(),
          coronaSerializer);
        sessions.put(sessionId, session);
        current = coronaSerializer.nextToken();
      }
      // Done with reading the END_OBJECT token for sessions
    }
docs: Reads back the sessions map from a JSON stream
  
  @param coronaSerializer The CoronaSerializer instance to be used to
  read the JSON
  @throws IOException