Steps to reproduce:

1. Upgraded to 4.0.28 from 4.0.27
2. Open any page with a graph and the graph does not render

ssl_error_log showing the following errors:

[Tue Jan 26 16:05:45.056986 2021] [:error] [pid 2215] [client 147.138.20.10:59572] PHP Parse error: syntax error, unexpected ':', expecting ';' or '{' in /usr/share/zabbix/include/classes/graphdraw/CLineGraphDraw.php on line 1305, referer: https://zabbix.bridgewater.edu/history.php?form_refresh=1&action=batchgraph&itemids%5B41633%5D=41633&itemids%5B41812%5D=41812&itemids%5B41816%5D=41816&graphtype=1

This error only started after the upgrade to 4.0.28