unjoin fails

[mdsumner]

library(tidyverse)
library(argosfilter)
library(sf)
data(seal)
seal_sf <- st_as_sf(seal, coords = c("lon","lat")) %>%
st_set_crs(4326)
seal_coords <- unlist(st_geometry(seal_sf)) %>%
matrix(ncol=2,byrow=TRUE) %>%
as_tibble() %>%
setNames(c("lon","lat"))
bind_cols(seal_sf,seal_coords) %>% head()
seal_coords
sfc_as_cols(seal_sf)
spbabel::sptable(seal_sf)
library(scsf)
PATH(seal_sf)

 Error in UseMethod("mutate_") : 
  no applicable method for 'mutate_' applied to an object of class "NULL" 

Use-case from sfr issue 231