api/documentation: Add a warning that nil may mean v:null

1 files changed, 4 insertions, 1 deletions

diff --git a/src/nvim/api/tabpage.c b/src/nvim/api/tabpage.c
index 475b75b571..3148a4fab7 100644
--- a/src/nvim/api/tabpage.c
+++ b/src/nvim/api/tabpage.c
@@ -60,7 +60,10 @@ Object tabpage_get_var(Tabpage tabpage, String name, Error *err)
 /// @param name The variable name
 /// @param value The variable value
 /// @param[out] err Details of an error that may have occurred
-/// @return The tab page handle
+/// @return The old value or nil if there was no previous value.
+///
+///         @warning It may return nil if there was no previous value
+///                  or if previous value was `v:null`.
 Object tabpage_set_var(Tabpage tabpage, String name, Object value, Error *err)
 {
   tabpage_T *tab = find_tab_by_handle(tabpage, err);