From 7967b1da0a38a188254a294401b708654fcc87a2 Mon Sep 17 00:00:00 2001
From: Utkarsh <utkarshpawadecse@gmail.com>
Date: Tue, 7 Apr 2026 16:10:59 +0530
Subject: [PATCH 1/2] validate empty list and zero-row matrix inputs in
 nuts_params.list()

---
 NEWS.md                          |  1 +
 R/bayesplot-extractors.R         |  8 ++++++++
 tests/testthat/test-extractors.R | 13 +++++++++++++
 3 files changed, 22 insertions(+)

diff --git a/NEWS.md b/NEWS.md
index c8f7d131f..99ec1f42e 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,6 @@
 # bayesplot (development version)
 
+* Validate empty list and zero-row matrix inputs in `nuts_params.list()`.
 * Replace `apply()` with `storage.mode()` for integer-to-numeric matrix conversion in `validate_predictions()`.
 * Fixed `is_chain_list()` to correctly reject empty lists instead of silently returning `TRUE`.
 * Added unit tests for `mcmc_areas_ridges_data()`, `mcmc_parcoord_data()`, and `mcmc_trace_data()`.
diff --git a/R/bayesplot-extractors.R b/R/bayesplot-extractors.R
index 19c6df882..d928224bc 100644
--- a/R/bayesplot-extractors.R
+++ b/R/bayesplot-extractors.R
@@ -145,10 +145,18 @@ nuts_params.stanreg <-
 #' @export
 #' @method nuts_params list
 nuts_params.list <- function(object, pars = NULL, ...) {
+  if (length(object) == 0) {
+    abort("'object' must be a non-empty list.")
+  }
+
   if (!all(sapply(object, is.matrix))) {
     abort("All list elements should be matrices.")
   }
 
+  if (nrow(object[[1]]) == 0) {
+    abort("All matrices in the list must have at least one row.")
+  }
+
   dd <- lapply(object, dim)
   if (length(unique(dd)) != 1) {
     abort("All matrices in the list must have the same dimensions.")
diff --git a/tests/testthat/test-extractors.R b/tests/testthat/test-extractors.R
index 53e9862cc..9f218e3f5 100644
--- a/tests/testthat/test-extractors.R
+++ b/tests/testthat/test-extractors.R
@@ -9,6 +9,8 @@ x <- list(cbind(a = 1:3, b = rnorm(3)), cbind(a = 1:3, b = rnorm(3)))
 
 # nuts_params and log_posterior methods -----------------------------------
 test_that("nuts_params.list throws errors", {
+  expect_error(nuts_params.list(list()), "non-empty list")
+
   x[[3]] <- c(a = 1:3, b = rnorm(3))
   expect_error(nuts_params.list(x), "list elements should be matrices")
 
@@ -17,6 +19,17 @@ test_that("nuts_params.list throws errors", {
 
   x[[3]] <- cbind(a = 1:4, b = rnorm(4))
   expect_error(nuts_params.list(x), "same dimensions")
+
+  zero_row <- list(cbind(a = numeric(0), b = numeric(0)))
+  expect_error(nuts_params.list(zero_row), "at least one row")
+})
+
+test_that("nuts_params.list works with single-chain list", {
+  single <- list(cbind(a = 1:3, b = rnorm(3)))
+  np <- nuts_params.list(single)
+  expect_identical(colnames(np), c("Chain", "Iteration", "Parameter", "Value"))
+  expect_true(all(np$Chain == 1L))
+  expect_equal(nrow(np), 6L)
 })
 
 test_that("nuts_params.list parameter selection ok", {

From 62389776acc53ce5aa16b40083ad7a08fa6b7638 Mon Sep 17 00:00:00 2001
From: Utkarsh <utkarshpawadecse@gmail.com>
Date: Tue, 7 Apr 2026 16:19:51 +0530
Subject: [PATCH 2/2] check zero-row matrices across all list elements in
 nuts_params.list()

---
 R/bayesplot-extractors.R         | 2 +-
 tests/testthat/test-extractors.R | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/R/bayesplot-extractors.R b/R/bayesplot-extractors.R
index d928224bc..c17bf45b4 100644
--- a/R/bayesplot-extractors.R
+++ b/R/bayesplot-extractors.R
@@ -153,7 +153,7 @@ nuts_params.list <- function(object, pars = NULL, ...) {
     abort("All list elements should be matrices.")
   }
 
-  if (nrow(object[[1]]) == 0) {
+  if (any(vapply(object, nrow, integer(1)) == 0)) {
     abort("All matrices in the list must have at least one row.")
   }
 
diff --git a/tests/testthat/test-extractors.R b/tests/testthat/test-extractors.R
index 9f218e3f5..74b9731a8 100644
--- a/tests/testthat/test-extractors.R
+++ b/tests/testthat/test-extractors.R
@@ -22,6 +22,9 @@ test_that("nuts_params.list throws errors", {
 
   zero_row <- list(cbind(a = numeric(0), b = numeric(0)))
   expect_error(nuts_params.list(zero_row), "at least one row")
+
+  zero_row_nonfirst <- list(cbind(a = 1:3, b = rnorm(3)), cbind(a = numeric(0), b = numeric(0)))
+  expect_error(nuts_params.list(zero_row_nonfirst), "at least one row")
 })
 
 test_that("nuts_params.list works with single-chain list", {