[libgda] Correction for bug #723777

[Vivien Malerba <vivien src gnome org>]

commit 1d4b91f7b251b80f4e9137b51cbc87b8199cb6f7
Author: Vivien Malerba <malerba gnome-db org>
Date:   Tue Feb 11 21:20:33 2014 +0100

    Correction for bug #723777

 libgda/gda-server-provider.c |   12 ++++++------
 1 files changed, 6 insertions(+), 6 deletions(-)
---
diff --git a/libgda/gda-server-provider.c b/libgda/gda-server-provider.c
index 85b6b92..2b9b9c3 100644
--- a/libgda/gda-server-provider.c
+++ b/libgda/gda-server-provider.c
@@ -437,11 +437,11 @@ gda_server_provider_set_impl_functions (GdaServerProviderClass *klass,
 gpointer
 _gda_server_provider_get_impl_functions (GdaServerProvider *provider, GdaWorker *worker, 
GdaServerProviderFunctionsType type)
 {
-       g_return_if_fail (GDA_IS_SERVER_PROVIDER (provider));
+       g_return_val_if_fail (GDA_IS_SERVER_PROVIDER (provider), NULL);
 
-       g_return_if_fail ((type >= 0) && (type < GDA_SERVER_PROVIDER_FUNCTIONS_MAX));
-       g_return_if_fail (worker);
-       g_return_if_fail (gda_worker_thread_is_worker (worker));
+       g_return_val_if_fail ((type >= 0) && (type < GDA_SERVER_PROVIDER_FUNCTIONS_MAX), NULL);
+       g_return_val_if_fail (worker, NULL);
+       g_return_val_if_fail (gda_worker_thread_is_worker (worker), NULL);
 
        return CLASS (provider)->functions_sets [type];
 }
@@ -458,8 +458,8 @@ _gda_server_provider_get_impl_functions (GdaServerProvider *provider, GdaWorker
 gpointer
 gda_server_provider_get_impl_functions_for_class (GObjectClass *klass, GdaServerProviderFunctionsType type)
 {
-       g_return_if_fail (GDA_IS_SERVER_PROVIDER_CLASS (klass));
-       g_return_if_fail ((type >= 0) && (type < GDA_SERVER_PROVIDER_FUNCTIONS_MAX));
+       g_return_val_if_fail (GDA_IS_SERVER_PROVIDER_CLASS (klass), NULL);
+       g_return_val_if_fail ((type >= 0) && (type < GDA_SERVER_PROVIDER_FUNCTIONS_MAX), NULL);
 
 #ifdef GDA_DEBUG_VIRTUAL
        g_print ("[V-klass] %s (klass=>%p, Class=>%s)\n", __FUNCTION__,