[niepce] fwk: make sure we don't pass a nullptr as a PropertyBag

[Hubert Figuière <hub src gnome org>]

commit 48ec61120d8e2f63d90c7636f9f105cc4ef86559
Author: Hubert Figuière <hub figuiere net>
Date:   Sun Feb 16 20:08:48 2020 -0500

    fwk: make sure we don't pass a nullptr as a PropertyBag

 src/fwk/toolkit/metadatawidget.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/src/fwk/toolkit/metadatawidget.cpp b/src/fwk/toolkit/metadatawidget.cpp
index c24eb12..776aead 100644
--- a/src/fwk/toolkit/metadatawidget.cpp
+++ b/src/fwk/toolkit/metadatawidget.cpp
@@ -241,7 +241,8 @@ void MetaDataWidget::set_data_source(const fwk::PropertyBagPtr& properties)
                           this->clear_widget(p);
                       });
     }
-    bool is_empty = fwk_property_bag_is_empty(properties.get());
+    bool is_empty =
+        static_cast<bool>(properties) ? fwk_property_bag_is_empty(properties.get()) : true;
     set_sensitive(!is_empty);
     if(is_empty) {
         return;