docs: Make documentation of disjoint_union() consistent with behavi…

…or (#1641)

.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$

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.
 #'

igraph.Rproj

@@ -1,4 +1,5 @@
 Version: 1.0
+ProjectId: ffa46ea4-a86f-4aac-9f09-64b2da845d3c
 
 RestoreWorkspace: No
 SaveWorkspace: No