the crash seems to happen whenever two underground pipes are next to each other on the pipelayer

this is the crash

24414.452 Error MainLoop.cpp:1282: Exception at tick 33418285: The mod Pipelayer (0.5.0) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event pipelayer::on_built_entity (ID 6)
__pipelayer__/Editor.lua:86: attempt to index local 'network' (a nil value)
stack traceback:
    __pipelayer__/Editor.lua:86: in function 'newest_connected_network'
    __pipelayer__/Editor.lua:101: in function 'connect_underground_pipe'
    __pipelayer__/Editor.lua:355: in function 'on_built_entity'
    __pipelayer__/control.lua:32: in function <__pipelayer__/control.lua:32>

save: https://drive.google.com/file/d/1YvgNBxFABorXdv1pWhOTdgalwGVXHlmk/view?usp=sharing
in the save to recreate this, just put a straight piece of pipe to connect with the underground ones

How were these underground pipes built? The internal state of Pipelayer is corrupted: these underground pipes don't have an associated network. You can show the network IDs by turning on the mod option, and if you do so, you can see that except for this collection of plastic pipe-to-grounds, everything else on the pipe layer has a network ID.

I'm not sure exactly which of the Picker Mods does it but my guess would be either Picker Belt Tools gives the underground pipe brush or it's Picker Pipe Tools. All I know is that after making a blueprint of 4 (grab one underground pipe, press Num+ 4 times until there are 4, then press Ctrl+Shift+R to create a span for them).

after making that span and placing down a bunch in a row pipelayer started freaking out when I tried to add any pipe to the existing pipe run. I also started the pipe run on the surface using Manifolds, so pump -> 5x1 manifold -> 5x Underground Pipe Connectors

not sure what part of that freaked out but i tried removing pipe and add it back in, but it seemed like placing any pipe anywhere in the line of pipes from the start to the end caused the crash

Probably an incompatibility with whichever Picker mod gave the underground brush. I’ll take a look.

Okay, the problem was with Picker Belt Tools. The way it works is it creates a blueprint in your cursor. When you click the blueprint is placed down, creating ghosts, and then Picker Belt Tools immediately revives those ghosts as if they were built by a construction robot. Since there's not supposed to be any way to get construction robots underground, Pipelayer wasn't handling the situation correctly.

This should now be fixed in v0.5.1. Any broken pipes in the underground that were created by Picker Belt Tools will be cleaned up and you will have to recreate them, but you can do so with Picker Belt Tools again and it should work.