Tree doesn't expand (Internal Server Error)

[ishibashi3]

i installed redmine_issues_tree 3.4.x on my redmine 3.4.13. (OS is CentOS Linux 7.8.2003)
but the tree doesn't expand and web server returned 500 (Internal Server Error).
below is Chrome F12 function.

■environment
Redmine version 3.4.13.stable
Ruby version 2.4.10-p364 (2020-03-31) [x86_64-linux]
Rails version 4.2.11.1
Environment production
Database adapter PostgreSQL

■Redmine's error.log
this occurs every time when i click "tree expand mark (▶) "

how can I solve this?
if there is any information that is missing, please let me know.