I just got this crash when pasting an inserter filter but accidentally clicked on a buffer chest.

The mod Filter Copying Expansion (1.6.0) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event filter-copy-expansion::FolterCopyExpansion_Paste (ID 207)
filter-copy-expansion/control.lua:540: attempt to index field '?' (a nil value)
stack traceback:
filter-copy-expansion/control.lua:540: in function <filter-copy-expansion/control.lua:37>

I made a fix in release V1.6.1 and V1.6.2, after inspection it looks like it could not be determined where to copy from.

This is however a patch, a copy should still occur because buffer/storage chests are supported.
Where did you copy from and did this entity have a filter enabled at the time? Maybe I could fix that as well.