关于return null 的疑惑

public Page<Record> getLogPages(String meter_id, Integer emi, Integer lack, Integer low, Integer close, 

			String stat, Integer page, Integer limit) throws Exception {

		String tbName = "data_civils_";

		if(StringUtils.isNotEmpty(stat))

			tbName += stat.replace("-", "").substring(0,6);

		else

			tbName += DateFormatUtils.format(new Date(), "yyyyMM");

		String tb = Db.queryStr("select table_name from information_schema.TABLES WHERE table_name = ?", tbName);

		if(StringUtils.isEmpty(tb))

			return null;

		else{

			String filter = getFilter(emi, lack, low, close, null, null);

			if(StringUtils.isNotEmpty(meter_id))

				filter += " and t.device_id = '" + meter_id + "'";

			if(StringUtils.isNotEmpty(stat))

				filter += " and t.stat_date = '" + stat + "'";

			String sql = "select count(1) from " + tbName + " t where 1=1";

			Long count = Db.queryLong(sql + filter);

			sql = "select t.stat_date, t.reading, t.voltage, t.surplus, t.balance, t.nouse, t.nosub, t.is_emi, t.is_lack, t.is_low, t.is_close, t.update_time,"

				+ " case when t.is_emi = 1 then 'red' else 'green' end color1, case when t.is_lack = 1 then 'red' else 'green' end color2,"

				+ " case when t.is_low = 1 then 'red' else 'green' end color3, case when t.is_close = 1 then 'red' else 'green' end color4"

				+ " from " + tbName + " t where 1=1" + filter + " order by t.stat_date desc limit ?,?";

			return new Page<Record>(page, limit, count, Db.find(sql, (page - 1) * limit, limit));

		}

	}

public Page<Record> getLogPages(Integer id, String stat, Integer page, Integer limit) throws Exception{

		String tbName = "data_cards_";

		if(StringUtils.isNotEmpty(stat))

			tbName += stat.replace("-", "").substring(0,6);

		else

			tbName += DateFormatUtils.format(new Date(), "yyyyMM");

		String tb = Db.queryStr("select table_name from information_schema.TABLES where table_name = ?", tbName);

		if(StringUtils.isEmpty(tb))

			return null;

		else{

			String filter = "";

			if(StringUtils.isNotBlank(stat))

				filter += " and stat_date = '" + stat.trim() + "'";

			if(id != null)

				filter += " and device_id = " + id;

			String sql = "select count(1) from tank." + tbName + " where 1=1";

			Long count = Db.queryLong(sql + filter);

			sql = "select * from tank." + tbName + " where 1=1 " + filter + " order by update_time desc limit ?,?";

			return new Page<Record>(page, limit, count, Db.find(sql, (page - 1) * limit, limit));

		}

	}