model_list <- add_expr(
  list(), 
  substitute(expr = {
  TRUE
  "A VERY VERY LONG STRINGA VERY VERY LONG STRINA VERY VERY LONG STRINA VERY VERY LONG STRINA VERY VERY LONG STRINA VERY VERY LONG STRINGGGGG"
}, env = list(
  data_model_fit = as.name(data_model_fit),
  aval_var = aval_var,
  split_covariates = split_covariates,
  id_var = id_var,
  arm_var = arm_var,
  visit_var = visit_var,
  cor_struct = cor_struct
)))