NPC could not save the portlets if switch to other TAB

[zhouleon]

Describe the bug
I update NPC to the current version 3.1, and Cacti is 1.2.8
NPC could not save the portlets if I switch to other TAB

To Reproduce
In NPC TAB, I could save the portlets.
If I switch to other TAB, Cacti will pop error message:

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Environment
Linux: Ubuntu 18.04 LST
Apache 2.4.29
MySQL 5.7.25-0ubuntu0.18.04.2
PHP 7.2.10-0ubuntu0.18.04.1
Nagios Core 4.4.5
Cacti 1.2.8