If MaterialsModule unexpected sees a part with DefaultTexture of null, log this with a warning.

OpenSim/Region/OptionalModules/Materials/MaterialsModule.cs

@@ -218,6 +218,10 @@ namespace OpenSim.Region.OptionalModules.Materials
 
             if (te.DefaultTexture != null)
                 GetStoredMaterialInFace(part, te.DefaultTexture);
+            else
+                m_log.WarnFormat(
+                    "[Materials]: Default texture for part {0} (part of object {1)) in {2} unexpectedly null.  Ignoring.", 
+                    part.Name, part.ParentGroup.Name, m_scene.Name);
 
             foreach (Primitive.TextureEntryFace face in te.FaceTextures)
             {