While upgrading Miniloaders :

The mod Upgrade Builder and Planner caused a non-recoverable error.
Please report this error to the mod author.

Error while running event upgrade-planner-next::on_player_selected_area (ID 49)
upgrade-planner-next/upgrade-planner/entity-upgrade.lua:16: attempt to index local 'new_entity_prototype' (a nil value)
stack traceback:
upgrade-planner-next/upgrade-planner/entity-upgrade.lua:16: in function 'create_new_entity_data'
upgrade-planner-next/upgrade-planner/entity-upgrade.lua:156: in function 'player_upgrade'
upgrade-planner-next/upgrade-planner/entity-upgrade.lua:325: in function 'upgrade_area_player'
upgrade-planner-next/control.lua:116: in function 'handler'
stdlib/stdlib/event/event.lua:315: in function 'pcall'
stdlib/stdlib/event/event.lua:335: in function 'dispatch_event'
stdlib/stdlib/event/event.lua:413: in function <stdlib/stdlib/event/event.lua:369>

Thanks for the report, I won't have time to look at it before the weekend.
Could you provide a short description of what you did or a screenshot.
Thanks!

Sure, i choose some normal stuff like belts and so on, and miniloader, then i choose the rectangle for the upgrad area, then the error pops up and then i am back in the main menu.

Fixed in latest version.

Works like charm, nice Christmas gift. thanks a lot.
Wish you happy holidays!