[glibmm] Pass 0 (NULL) instead of for C properties.

[Murray Cumming <murrayc src gnome org>]

commit db1668a39d9646882d5aa6b7386a3b7ea70f99af
Author: Murray Cumming <murrayc murrayc com>
Date:   Tue Sep 3 21:40:25 2013 +0200

    Pass 0 (NULL) instead of  for C properties.
    
    * glib/glibmm/objectbase.cc: set_property_value():
    * glib/glibmm/propertyproxy_base.cc: set_property():
      If the value is a G_TYPE_STRING (a gchar*), and is "",
      then pass 0 instead.
      Bug #686909

 glib/glibmm/objectbase.cc         |   12 ++++++++++++
 glib/glibmm/propertyproxy_base.cc |   15 ++++++++++++++-
 2 files changed, 26 insertions(+), 1 deletions(-)
---
diff --git a/glib/glibmm/objectbase.cc b/glib/glibmm/objectbase.cc
index 140816a..047f192 100644
--- a/glib/glibmm/objectbase.cc
+++ b/glib/glibmm/objectbase.cc
@@ -260,6 +260,18 @@ bool ObjectBase::_cpp_destruction_is_in_progress() const
 
 void ObjectBase::set_property_value(const Glib::ustring& property_name, const Glib::ValueBase& value)
 {
+  const GValue* cvalue = value.gobj();
+  if(cvalue && G_VALUE_HOLDS(cvalue, G_TYPE_STRING))
+  {
+    const gchar* str = g_value_get_string (cvalue);
+    if(str && (strcmp(str, "") == 0))
+    {
+      //Pass NULL to the C API instead of "":
+      g_object_set(gobj(), property_name.c_str(), (void*)0, (void*)0);
+      return;
+    }
+  }
+
   g_object_set_property(gobj(), property_name.c_str(), value.gobj());
 }
 
diff --git a/glib/glibmm/propertyproxy_base.cc b/glib/glibmm/propertyproxy_base.cc
index 0f1fac8..4274c65 100644
--- a/glib/glibmm/propertyproxy_base.cc
+++ b/glib/glibmm/propertyproxy_base.cc
@@ -26,6 +26,7 @@
 #include <glibmm/signalproxy_connectionnode.h>
 #include <glibmm/object.h>
 #include <glibmm/private/object_p.h>
+#include <cstring>
 
 namespace Glib
 {
@@ -98,7 +99,19 @@ SignalProxyProperty PropertyProxy_Base::signal_changed()
 
 void PropertyProxy_Base::set_property_(const Glib::ValueBase& value)
 {
-  g_object_set_property(obj_->gobj(), property_name_, value.gobj());
+  const GValue* cvalue = value.gobj();
+  if(cvalue && G_VALUE_HOLDS(cvalue, G_TYPE_STRING))
+  {
+    const gchar* str = g_value_get_string (cvalue);
+    if(str && (strcmp(str, "") == 0))
+    {
+      //Pass NULL to the C API instead of "":
+      g_object_set(obj_->gobj(), property_name_, (void*)0, (void*)0);
+      return;
+    }
+  }
+
+  g_object_set_property(obj_->gobj(), property_name_, cvalue);
 }
 
 void PropertyProxy_Base::get_property_(Glib::ValueBase& value) const