From c5358ee3072266c2550bf18ca2e95da589d89e09 Mon Sep 17 00:00:00 2001
From: jrheinlaender <jrheinlaender@users.sourceforge.net>
Date: Sun, 7 Jul 2013 11:29:16 +0200
Subject: [PATCH] Prevent unknown exception thrown while loading a part

---
 src/Mod/PartDesign/App/DatumPlane.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/Mod/PartDesign/App/DatumPlane.cpp b/src/Mod/PartDesign/App/DatumPlane.cpp
index fec4ff5bc..9f95deb7f 100644
--- a/src/Mod/PartDesign/App/DatumPlane.cpp
+++ b/src/Mod/PartDesign/App/DatumPlane.cpp
@@ -182,10 +182,14 @@ void Plane::onChanged(const App::Property *prop)
     if (prop == &References) {
         refTypes.clear();
         std::vector<App::DocumentObject*> refs = References.getValues();
-        std::vector<std::string> refnames = References.getSubValues();
+        std::vector<std::string> refnames = References.getSubValues();        
 
-        for (int r = 0; r < refs.size(); r++)
+        for (int r = 0; r < refs.size(); r++) {
+            const Part::Feature* ref = static_cast<const Part::Feature*>(refs[r]);
+            if ((ref != NULL) && ref->Shape.getValue().IsNull())
+                continue; // This can happen while a document is being restored from a file
             refTypes.insert(getRefType(refs[r], refnames[r]));
+        }
 
         if (fabs(Angle.getValue()) > Precision::Confusion())
             refTypes.insert(ANGLE);