#vulnerable code 
                                public static void refresh(final DataSourceProxy dataSourceProxy){
        ConcurrentMap<String, TableMeta> tableMetaMap = TABLE_META_CACHE.asMap();
        for (Entry<String, TableMeta> entry : tableMetaMap.entrySet()) {
            try {
                TableMeta tableMeta = fetchSchema(dataSourceProxy, entry.getValue().getTableName());
                if (tableMeta == null){
                    LOGGER.error("get table meta error");
                }
                if (!tableMeta.equals(entry.getValue())){
                    TABLE_META_CACHE.put(entry.getKey(), tableMeta);
                    LOGGER.info("table meta change was found, update table meta cache automatically.");
                }
            } catch (SQLException e) {
                LOGGER.error("get table meta error:{}", e.getMessage(), e);
            }
        }
    } 
                            #location 9 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public static void refresh(final DataSourceProxy dataSourceProxy){
        ConcurrentMap<String, TableMeta> tableMetaMap = TABLE_META_CACHE.asMap();
        for (Entry<String, TableMeta> entry : tableMetaMap.entrySet()) {
            String key = getCacheKey(dataSourceProxy, entry.getValue().getTableName());
            if(entry.getKey().equals(key)){
                try {
                    TableMeta tableMeta = fetchSchema(dataSourceProxy, entry.getValue().getTableName());
                    if (!tableMeta.equals(entry.getValue())){
                        TABLE_META_CACHE.put(entry.getKey(), tableMeta);
                        LOGGER.info("table meta change was found, update table meta cache automatically.");
                    }
                } catch (SQLException e) {
                    LOGGER.error("get table meta error:{}", e.getMessage(), e);
                }
            }
        }
    }