Mirko Vukovic <mirko.vukovic@gmail.com> writes:

> My current workflow is
>
>    1. Enter edit buffer (C-c ')
>    2. Perform edits in the window
>    3. Exit edit mode (C-c ')
>    4. Evaluate code (C-c C-c)
>    5. Monitor changes to resulting png file
>
> I would prefer instead to skip step 3, and evaluate the code from within
> the edit mode.
>
> Is it possible to execute code from the edit buffer?

1. When I enter the edit mode (C-c ') it connects to plantuml server
(that I don't like), and produces the error that you have specified:
"Wrong type argument: stringp, nil".

2. Pressing C-c C-c in the edit buffer opens up plantuml preview but it
gives some error: "The plugin you are using seems to generate a bad
URL".

I am on Emacs 28.x and default org 9.3.