[libgnome-volume-control] Add missing allow-none annotations

[Bastien Nocera <hadess src gnome org>]

commit b28ae07ae1a96a98d4363fd8eacb69ab9bb6a806
Author: Robert Ancell <robert ancell canonical com>
Date:   Fri Mar 15 09:47:00 2019 +1300

    Add missing allow-none annotations

 gvc-mixer-card.c      | 9 +++++++++
 gvc-mixer-control.c   | 2 +-
 gvc-mixer-ui-device.c | 2 +-
 3 files changed, 11 insertions(+), 2 deletions(-)
---
diff --git a/gvc-mixer-card.c b/gvc-mixer-card.c
index 0856493..93be4da 100644
--- a/gvc-mixer-card.c
+++ b/gvc-mixer-card.c
@@ -220,6 +220,15 @@ _pa_context_set_card_profile_by_index_cb (pa_context                       *cont
         card->priv->profile_op = NULL;
 }
 
+/**
+ * gvc_mixer_card_change_profile:
+ * @card: a #GvcMixerCard
+ * @profile: (allow-none): the profile to change to or %NULL.
+ *
+ * Change the profile in use on this card.
+ *
+ * Returns: %TRUE if profile successfully changed or already using this profile.
+ */
 gboolean
 gvc_mixer_card_change_profile (GvcMixerCard *card,
                                const char *profile)
diff --git a/gvc-mixer-control.c b/gvc-mixer-control.c
index 78d5cf2..de1c574 100644
--- a/gvc-mixer-control.c
+++ b/gvc-mixer-control.c
@@ -518,7 +518,7 @@ gvc_mixer_control_get_stream_from_device (GvcMixerControl *control,
  * gvc_mixer_control_change_profile_on_selected_device:
  * @control:
  * @device:
- * @profile: Can be null if any profile present on this port is okay
+ * @profile: (allow-none): Can be %NULL if any profile present on this port is okay
  *
  * Returns: This method will attempt to swap the profile on the card of
  * the device with given profile name.  If successfull it will set the
diff --git a/gvc-mixer-ui-device.c b/gvc-mixer-ui-device.c
index 67fb792..9b6addc 100644
--- a/gvc-mixer-ui-device.c
+++ b/gvc-mixer-ui-device.c
@@ -447,7 +447,7 @@ gvc_mixer_ui_device_set_profiles (GvcMixerUIDevice *device,
 
 /**
  * gvc_mixer_ui_device_get_best_profile:
- * @selected: The selected profile or its canonical name or %NULL for any profile
+ * @selected: (allow-none): The selected profile or its canonical name or %NULL for any profile
  * @current: The currently selected profile
  *
  * Returns: (transfer none): a profile name, valid as long as the UI device profiles are.