Check explicitly

R-package/R/xgb.model.dt.tree.R

@@ -134,7 +134,10 @@ xgb.model.dt.tree <- function(feature_names = NULL, model = NULL, text = NULL,
   ]
 
   # assign feature_names when available
-  if (!is.null(feature_names) && !is.na(td$Feature)) {
+  is_stump <- function() {
+    return(length(td$Feature) == 1 && is.na(td$Feature))
+  }
+  if (!is.null(feature_names) && !is_stump()) {
     if (length(feature_names) <= max(as.numeric(td$Feature), na.rm = TRUE))
       stop("feature_names has less elements than there are features used in the model")
     td[isLeaf == FALSE, Feature := feature_names[as.numeric(Feature) + 1]]

R-package/tests/testthat/test_helpers.R

@@ -340,6 +340,16 @@ test_that("xgb.importance works with and without feature names", {
     imp
   }
   expect_equal(importance_from_dump(), importance, tolerance = 1e-6)
+
+  ## decision stump
+  m <- xgboost::xgboost(
+    data = as.matrix(data.frame(x = c(0, 1))),
+    label = c(1, 2),
+    nrounds = 1
+  )
+  df <- xgb.model.dt.tree(model = m)
+  expect_equal(df$Feature, "Leaf")
+  expect_equal(df$Cover, 2)
 })
 
 test_that("xgb.importance works with GLM model", {