when I view last data --> chart -->last 7 day grah chat,  there is an error in nginx error.log, follow this :

2021/07/16 15:59:45 [error] 18532#0: *36354510 FastCGI sent in stderr: "PHP message: PHP Fatal error: Uncaught ValueError: bcdiv(): Argument #1 ($num1) is not well-formed in /opt/nginx/html/zabbix/include/classes/graphdraw/CLineGraphDraw.php:368
Stack trace:
#0 /opt/nginx/html/zabbix/include/classes/graphdraw/CLineGraphDraw.php(368): bcdiv('-9.999999999621...', '5')
#1 /opt/nginx/html/zabbix/include/classes/graphdraw/CLineGraphDraw.php(2554): CLineGraphDraw->selectData()
#2 /opt/nginx/html/zabbix/chart.php(147): CLineGraphDraw->draw()
#3

thrown in /opt/nginx/html/zabbix/include/classes/graphdraw/CLineGraphDraw.php on line 368" while reading response header from upstream, client: 10.1.64.51, server: localhost, request: "GET /zabbix/chart.php?from=2021-07-15%2011%3A00%3A00&to=2021-07-15%2012%3A00%3A00&itemids%5B0%5D=49869&type=0&profileIdx=web.item.graph.filter&profileIdx2=49869&width=1302&height=200&_=uwsbvpmq&screenid= HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "10.1.64.120:1080", referrer: "http://10.1.64.120:1080/zabbix/history.php?action=showgraph&itemids[]=49869"

how can I resovle it .. pls ~ give me some help ~thanks verymuch