Error calling stpm2 method within user define method

I've written a method that takes a formula as an argument that then gets passed to stpm2. If my method's parameter is not named "formula" then I get an error. See below example:

sesssionInfo()

R version 3.5.1 (2018-07-02)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows >= 8 x64 (build 9200)

Matrix products: default

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252    LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C                           LC_TIME=English_United States.1252    

attached base packages:
[1] splines   stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] rstpm2_1.4.4    survival_2.42-3

loaded via a namespace (and not attached):
 [1] compiler_3.5.1    Matrix_1.2-14     tools_3.5.1       mgcv_1.8-24       yaml_2.2.0        Rcpp_1.0.0        bbmle_1.0.20     
 [8] nlme_3.1-137      grid_3.5.1        numDeriv_2016.8-1 stats4_3.5.1      lattice_0.20-35

Reproducible example:

library(rstpm2)

data(brcancer)

# Function with model_formula paramter **ERRORS**
f_bad <- function(model_formula) {

  stpm2(formula = model_formula, df = 2, data=brcancer, link.type = "PH")
}

# Function with formula paramter to match the name pf stpm2's formula parameter **PASSES**
f_good <- function(formula) {

  stpm2(formula = formula, df = 2, data=brcancer, link.type = "PH")
}

f_bad (model_formula = Surv(rectime,censrec==1)~hormon)
f_good (formula = Surv(rectime,censrec==1)~hormon)

mclements / rstpm2

Error calling stpm2 method within user define method #11