Error in private$reset_batch() : attempt to apply non-function

[niehu2018]

Refer to https://satijalab.org/loomr/loomr_tutorial

when I run
lfile$map(FUN = rowSums, chunk.size = 500)
It report "Error in private$reset_batch() : attempt to apply non-function"

So, what should I do to get the right result