Error in call2 when using local fit function and omitting pkg

[chillerb]

The problem

According to the parsnip tutorial, pkg is not required to use a local function for fitting:

func is the package and name of the function that will be called. If you are using a locally defined function, only fun is required.

However, if I try to register a model with a local fit function, I receive an error in call2, that namespace ns should be a string.
I am quite new to tidymodels, am I missing something?

Reproducible example

library(tidymodels)

set_new_model("my_model")

set_model_mode(model = "my_model", mode = "regression")

set_model_engine(
  "my_model", 
  mode = "regression", 
  eng = "my_engine"
)

my_model <-
  function(mode = "regression") {
    # Check for correct mode
    if (mode  != "regression") {
      rlang::abort("`mode` should be 'regression'.")
    }
    
    # Save some empty slots for future parts of the specification
    new_model_spec(
      "my_model",
      args = list(),
      eng_args = NULL,
      mode = mode,
      method = NULL,
      engine = NULL
    )
  }

my_model_fun <- function(...) {
  print(list(...))
}

set_fit(
  model = "my_model",
  eng = "my_engine",
  mode = "regression",
  value = list(
    interface = "matrix",
    # should not be changeable by the user
    protect = c("formula", "data"),
    func = c(fun = "my_model_fun"),
    defaults = list()
  )
)

my_model() %>%
  translate("my_engine")
#> my model Model Specification (regression)
#> 
#> Computational engine: my_engine 
#> 
#> Model fit template:
#> Error in `call2()` at parsnip/R/misc.R:245:3:
#> ! `ns` must be a string

^{Created on 2025-01-16 with reprex v2.1.1}

Session info

sessioninfo::session_info()
#> ─ Session info ───────────────────────────────────────────────────────────────
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#>  date     2025-01-16
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#> ─ Packages ───────────────────────────────────────────────────────────────────
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#> 
#>  [1] /root/.cache/R/renv/library/rabaki-e6dba559/linux-ubuntu-jammy/R-4.4/x86_64-pc-linux-gnu
#>  [2] /root/.cache/R/renv/sandbox/linux-ubuntu-jammy/R-4.4/x86_64-pc-linux-gnu/25ebdc09
#>  [3] /usr/local/lib/R/library
#> 
#>  P ── Loaded and on-disk path mismatch.
#> 
#> ──────────────────────────────────────────────────────────────────────────────

[chillerb]

The error seems to originate from:

#' Print the model call
#'
#' @param object A "model_spec" object.
#' @return A character string.
#' @keywords internal
#' @export
show_call <- function(object) {
  object$method$fit$args <-
    map(object$method$fit$args, convert_arg)

  call2(object$method$fit$func["fun"],
    !!!object$method$fit$args,
    .ns = object$method$fit$func["pkg"]
  )
}

I noticed that the pkg name is NA, if pkg is not passed or even explicitly set to pkg=NULL:

`> object$method$fit$func["pkg"]
<NA> 
  NA 

Is this intended? Call2 works for .ns = NULL, but fails for .ns = NA.

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