Unhandled errors must error properly (#797)

R-package/R/lgb.Booster.R

@@ -32,6 +32,10 @@ Booster <- R6Class(
       params <- append(params, list(...))
       params_str <- lgb.params2str(params)
       handle <- 0.0
+      
+      # Attempts to create a handle for the dataset
+      try({
+        
         # Check if training dataset is not null
         if (!is.null(train_set)) {
           
@@ -92,9 +96,16 @@ Booster <- R6Class(
           stop("lgb.Booster: Need at least either training dataset, model file, or model_str to create booster instance")
           
         }
+        
+      })
+      
+      # Check whether the handle was created properly if it was not stopped earlier by a stop call
       if (lgb.is.null.handle(handle)) {
+        
         stop("lgb.Booster: cannot create Booster handle")
+        
       } else {
+        
         # Create class
         class(handle) <- "lgb.Booster.handle"
         private$handle <- handle
@@ -102,6 +113,7 @@ Booster <- R6Class(
         private$num_class <- lgb.call("LGBM_BoosterGetNumClasses_R",
                                       ret = private$num_class,
                                       private$handle)
+        
       }
       
     },