Report module issue with complex expressions

[rouhu]

Espocrm v.9.1.9
Advance Pack v3.11.9
MariaDB v10.5
PHP 8.3

Steps to reproduce:
Create a grid report, add name field and add any complex expression for it:
LOWERname)

This report column comes empty and the log will show error:

[2025-10-16 08:19:59] ERROR:
[2025-10-16 08:19:59] WARNING: E_WARNING: Undefined array key "__STUB__"
[2025-10-16 08:19:59] WARNING: E_WARNING: Undefined array key "__STUB__"
[2025-10-16 08:19:59] WARNING: E_WARNING: Undefined array key "__STUB__"
...

[yuri]

Unfortunaltey, complex expressions in sub-group columns currently are not supported.