Error while running event blueprint-request::on_gui_click (ID 1)
blueprint-request/control.lua:131: bad argument #1 of 2 to 'pairs' (table expected, got nil)
stack traceback:
[C]: in function 'pairs'
blueprint-request/control.lua:131: in function 'collect_items'
blueprint-request/control.lua:50: in function <blueprint-request/control.lua:41>

Do you have a blueprint string I can reproduce it with?

The blueprint contains entities that are indeed not directly placable. From a mod train stop that is made of several entities. Adding a "if replacements" around the for loop fixes the problem for me. I think it should not do any harm to do so.

A simple blueprint that should trigger the problem is below. But it requires the "cargo train manager" mod to be installed. It might be possible to trigger it with logistics train manager stops - the same type of train stops are used there - but I have not used this mod in a while so maybe not.

0eNqNk91ugzAMhd/F11CtUPrDxZ5id9OEUnBpJEgix6mGKt59CdG6rqNr73Bin8/HOGfYdw4NScVQnkHWWlko389gZatEF854MAglSMYeElCiDxEJ2cGYgFQNfkK5HJOHJexrVGpZm6vCbPxIABVLlhjBUzBUyvV7JK98qa8FtTqNKr1QokWa1FLt2Dj2IKOt19EqtBCa2mWLIoHBf212i8JDG0lYx4x16PiGlT1mdaI3/5O2E8nPkUl31R6P4iQ1hcRaUu0kV/6uuVQfJFmu/ozuJImdP7l0FDNSoQY+StVCZFgW4ce9hKA3ggQHFLyGa2fRozpNfq5MDscZx/lDx3Nm8++h3ox03jahaKoD6b6a1GMzSVyHKiAMNs8P4A28D/C+IxNgxtXqpyhQ2iOn077et7Jd/raSzagWz6sW91T9sk+Porx6dgmckGxM2C5Xm122WWV5vi3W4/gFn985AQ==

Fixed