public Optional<ShardingTable> findShardingTable(final String logicTableName) {
        if (Strings.isNullOrEmpty(logicTableName) || !shardingTables.containsKey(logicTableName)) {
            return Optional.empty();
        }
        return Optional.of(shardingTables.get(logicTableName));
    }
@Test
    void assertNotFindTableRuleWhenTableNameIsNull() {
        assertFalse(createMaximumShardingRule().findShardingTable(null).isPresent());
    }