bind_rows() correctly handles consecutive NULLs.

closes tidyverse#4296

NEWS.md

@@ -25,6 +25,8 @@
 
 * `group_map()` now only calls the function on each group and return a list. 
 
+* `bind_rows()` correctly handles the cases where there are multiple consecutive `NULL` (#4296). 
+
 # dplyr 0.8.0.1 (2019-02-15)
 
 * Fixed integer C/C++ division, forced released by CRAN (#4185). 

src/bind.cpp

@@ -264,7 +264,7 @@ Rcpp::List rbind__impl(Rcpp::List dots, const dplyr::SymbolString& id) {
       SEXP* p_dots_names = STRING_PTR(dots_names);
       SEXP* p_dots = get_vector_ptr(dots);
 
-      // we id_col now, so it is definitely younger than dots_names
+      // we create id_col now, so it is definitely younger than dots_names
       // this is surely write barrier proof
       SEXP id_col = PROTECT(Rf_allocVector(STRSXP, n));
 
@@ -273,7 +273,7 @@ Rcpp::List rbind__impl(Rcpp::List dots, const dplyr::SymbolString& id) {
 
         // skip NULL on dots. because the way df_nrows is made above
         // need to skip dots_names too
-        if (Rf_isNull(*p_dots)) {
+        while (Rf_isNull(*p_dots)) {
           ++p_dots;
           ++p_dots_names;
         }

tests/testthat/test-rbind.R

@@ -315,3 +315,16 @@ test_that("bind_rows warns on binding factor and character (#1485)", {
   df2 <- tail(iris, 1) %>% mutate(Species = as.character(Species))
   expect_warning(bind_rows(df1, df2), "binding factor and character vector, coercing into character vector")
 })
+
+test_that("bind_rows() correctly handles consecutive NULLs (#4296)", {
+  res <- list(
+    a = tibble(expected_id = "a"),
+    b = NULL,
+    c = NULL,
+    d = tibble(expected_id = "d"),
+    c = NULL,
+    e = tibble(expected_id = "e")
+  ) %>%
+    bind_rows(.id = "id")
+  expect_equal(res$id, res$expected_id)
+})