[R-package] remove broken default for `file` in readRDS / saveRDS functions (#3664)

* [R-package] remove broken default file in readRDS / saveRDS functions

* empty commit

.gitignore

@@ -404,6 +404,9 @@ python-package/lightgbm/VERSION.txt
 **/autom4te.cache/
 conftest*
 R-package/config.status
+!R-package/data/agaricus.test.rda
+!R-package/data/agaricus.train.rda
+!R-package/data/bank.rda
 R-package/docs
 R-package/src/CMakeLists.txt
 R-package/src/Makevars
@@ -422,9 +425,7 @@ miktex*.zip
 
 # Files created by R examples and tests
 **/lgb-Dataset.data
-**/lgb-model.rds
 **/lgb.Dataset.data
-**/model.rds
 **/model.txt
 **/lgb-model.txt
 
@@ -432,6 +433,9 @@ miktex*.zip
 .Rproj.user
 **/.Rapp.history
 **/.Rhistory
+*.rda
+*.RData
+*.rds
 
 # Files generated by aspell
 **/*.bak

R-package/R/readRDS.lgb.Booster.R

@@ -31,7 +31,7 @@
 #' new_model <- readRDS.lgb.Booster(model_file)
 #' }
 #' @export
-readRDS.lgb.Booster <- function(file = "", refhook = NULL) {
+readRDS.lgb.Booster <- function(file, refhook = NULL) {
 
   object <- readRDS(file = file, refhook = refhook)
 

R-package/R/saveRDS.lgb.Booster.R

@@ -42,7 +42,7 @@
 #' }
 #' @export
 saveRDS.lgb.Booster <- function(object,
-                                file = "",
+                                file,
                                 ascii = FALSE,
                                 version = NULL,
                                 compress = TRUE,

R-package/man/readRDS.lgb.Booster.Rd

@@ -4,7 +4,7 @@
 \alias{readRDS.lgb.Booster}
 \title{readRDS for \code{lgb.Booster} models}
 \usage{
-readRDS.lgb.Booster(file = "", refhook = NULL)
+readRDS.lgb.Booster(file, refhook = NULL)
 }
 \arguments{
 \item{file}{a connection or the name of the file where the R object is saved to or read from.}

R-package/man/saveRDS.lgb.Booster.Rd

@@ -6,7 +6,7 @@
 \usage{
 saveRDS.lgb.Booster(
   object,
-  file = "",
+  file,
   ascii = FALSE,
   version = NULL,
   compress = TRUE,