diff --git a/.Rbuildignore b/.Rbuildignore
index 073411ed5d..11ed100330 100644
--- a/.Rbuildignore
+++ b/.Rbuildignore
@@ -51,9 +51,9 @@
 ^R/revdep\.R$
 ^compile_commands\.json$
 ^\.cache$
+^rchk$
 ^man/dot-igraph.progress\.Rd$
 ^man/dot-igraph.status\.Rd$
 ^man/dot-extract_constructor_and_modifiers\.Rd$
 ^man/dot-apply_modifiers\.Rd$
 ^man/handle_vertex_type_arg\.Rd$
-^rchk$
diff --git a/R/operators.R b/R/operators.R
index 965f983e8f..f0a37d1d47 100644
--- a/R/operators.R
+++ b/R/operators.R
@@ -172,10 +172,11 @@ rename.attr.if.needed <- function(type, graphs, newsize = NULL, maps = NULL,
 #' have completely disjoint graphs. Then a simple union is created. This
 #' function can also be used via the `%du%` operator.
 #'
-#' `graph.disjont.union` handles graph, vertex and edge attributes.  In
-#' particular, it merges vertex and edge attributes using the basic `c()`
+#' `disjoint_union()` handles graph, vertex and edge attributes.  In
+#' particular, it merges vertex and edge attributes using the [vctrs::vec_c()]
 #' function. For graphs that lack some vertex/edge attribute, the corresponding
-#' values in the new graph are set to `NA`. Graph attributes are simply
+#' values in the new graph are set to a missing value (`NA` for scalar attributes,
+#' `NULL` for list attributes). Graph attributes are simply
 #' copied to the result. If this would result a name clash, then they are
 #' renamed by adding suffixes: _1, _2, etc.
 #'
diff --git a/igraph.Rproj b/igraph.Rproj
index f11d3659d3..4b440dd1fb 100644
--- a/igraph.Rproj
+++ b/igraph.Rproj
@@ -1,4 +1,5 @@
 Version: 1.0
+ProjectId: ffa46ea4-a86f-4aac-9f09-64b2da845d3c
 
 RestoreWorkspace: No
 SaveWorkspace: No
diff --git a/man/closeness.Rd b/man/closeness.Rd
index 0502a7f28f..dc860d003e 100644
--- a/man/closeness.Rd
+++ b/man/closeness.Rd
@@ -43,7 +43,7 @@ Numeric vector with the closeness values of all the vertices in
 \code{v}.
 }
 \description{
-Closeness centrality measures how many steps is required to access every other
+Closeness centrality measures how many steps are required to access every other
 vertex from a given vertex.
 }
 \details{
diff --git a/man/disjoint_union.Rd b/man/disjoint_union.Rd
index 8bd0cc2c69..626248720e 100644
--- a/man/disjoint_union.Rd
+++ b/man/disjoint_union.Rd
@@ -27,10 +27,11 @@ Thus first the vertices in the second, third, etc. graphs are relabeled to
 have completely disjoint graphs. Then a simple union is created. This
 function can also be used via the \verb{\%du\%} operator.
 
-\code{graph.disjont.union} handles graph, vertex and edge attributes.  In
-particular, it merges vertex and edge attributes using the basic \code{c()}
+\code{disjoint_union()} handles graph, vertex and edge attributes.  In
+particular, it merges vertex and edge attributes using the \code{\link[vctrs:vec_c]{vctrs::vec_c()}}
 function. For graphs that lack some vertex/edge attribute, the corresponding
-values in the new graph are set to \code{NA}. Graph attributes are simply
+values in the new graph are set to a missing value (\code{NA} for scalar attributes,
+\code{NULL} for list attributes). Graph attributes are simply
 copied to the result. If this would result a name clash, then they are
 renamed by adding suffixes: _1, _2, etc.