[libhandy] Revert "expander-row: Make the subtitle nullable"

[Alexander Mikhaylenko <alexm src gnome org>]

commit 5e59ffc0c3aaf5de55bfff82b86e7eb5ccdffbbd
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Wed Jul 29 17:14:20 2020 +0500

    Revert "expander-row: Make the subtitle nullable"
    
    This reverts commit fdd9c2651c053eaba94287fb1335a09da4c59093.

 src/hdy-expander-row.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/hdy-expander-row.c b/src/hdy-expander-row.c
index 55bf6952..a6a7f5e1 100644
--- a/src/hdy-expander-row.c
+++ b/src/hdy-expander-row.c
@@ -440,7 +440,7 @@ hdy_expander_row_new (void)
  *
  * Gets the subtitle for @self.
  *
- * Returns: (transfer none) (nullable): the subtitle for @self, or %NULL.
+ * Returns: the subtitle for @self.
  *
  * Since: 1.0
  */
@@ -459,7 +459,7 @@ hdy_expander_row_get_subtitle (HdyExpanderRow *self)
 /**
  * hdy_expander_row_set_subtitle:
  * @self: a #HdyExpanderRow
- * @subtitle: (nullable): the subtitle
+ * @subtitle: the subtitle
  *
  * Sets the subtitle for @self.
  *