Cryptic error in data.R if NULL passed as a variable #1126
Description
Describe the bug
If the data provided as a list includes a variable of type NULL, this won't be detected and the cryptic error as follows is generated:
Error in round(x) : non-numeric argument to mathematical function
(I had a bug in my own data prep code that meant NULL was being passed as a variable in the list without my awareness and because this error was so vague it took some time to track down the problem)
To Reproduce
library(cmdstanr)
file <- file.path(cmdstan_path(), "examples/bernoulli/bernoulli.stan")
mod <- cmdstan_model(file)
# data including a NULL variable
stan_data <- list(N = NULL, y = c(0,1,0,0,0,0,0,0,0,1))
# Run MCMC using the 'sample' method
fit_mcmc <- mod$sample(data = stan_data)
Expected behavior
It would be preferable if an error reported "Variable 'N' was found to be NULL - numeric value expected.' - or something along those lines.
Operating system
Mac OsX 26.2
CmdStanR version number
‘0.9.0.9000’
CmdStan version 2.37
Additional context
On some occasions (though I could not make a reprex for this), the error also included the text:
Error in round(x) : non-numeric argument to mathematical function
Called from: is_wholenumber(data[[var_name]])
I searched for is_wholenumber in CmdStanR source code and found it only once in the process_data function at line 190 in the data.R file - so I believe this line is throwing the error at least some of the time if not all.