Support for NULL tensors.

src/tensor.cpp

@@ -128,6 +128,12 @@ torch::Tensor torch_tensor_cpp(SEXP x, Rcpp::Nullable<torch::Dtype> dtype,
         break;
       }
     }
+  case NILSXP: {
+      cdtype = lantern_Dtype_bool();
+      final_type = dtype.isNull() ? torch::Dtype(lantern_Dtype_bool())
+        : Rcpp::as<torch::Dtype>(dtype);
+      break;
+    }
     default: {
       Rcpp::stop("R type not handled");
     }

tests/testthat/test-indexing.R

@@ -250,3 +250,15 @@ test_that("regression test for #695", {
     as.array(a)[c(1, 3), , c(1, 3)]
   )
 })
+
+test_that("NULL tensor", {
+
+  x <- torch_tensor(NULL)
+  expect_true(x$dtype == torch_bool())
+  expect_equal(x$shape, 0)
+
+  # subsetting shouldn't crash
+  expect_error(x[1], regexp = "out of bounds")
+  expect_error(torch_tensor(as.integer(NULL))[1], regexp = "out of bounds")
+
+})