BUG #16000: PgAdmin 4.12 Internal Server Error

The following bug has been logged on the website:

Bug reference:      16000
Logged by:          Cees van Zeeland
Email address:      cees.van.zeeland@xs4all.nl
PostgreSQL version: 11.5
Operating system:   Windows 10
Description:

Hello,

This seems to be a bug in PgAdmin 4.12 

When I select any View and then click on the SQL tab I get a popup
“Internal Server Error”
With the message “can only concatenate str (not "NoneType") to str”

The View itself works fine. 
Earlier versions of PgAdmin 4  did not show this error.

It might be related to Python?

I hope this message will reach the developers.

Thanks for any help,

Cees van Zeeland