Fix bug where unlinking a style that was invalidly linked didn't work.

src/blenderbim/blenderbim/tool/style.py

@@ -46,7 +46,10 @@ class Style(blenderbim.core.tool.Style):
     @classmethod
     def get_style(cls, obj):
         if obj.BIMMaterialProperties.ifc_style_id:
-            return tool.Ifc.get().by_id(obj.BIMMaterialProperties.ifc_style_id)
+            try:
+                return tool.Ifc.get().by_id(obj.BIMMaterialProperties.ifc_style_id)
+            except:
+                return
 
     @classmethod
     def get_surface_rendering_attributes(cls, obj):

src/blenderbim/test/tool/test_style.py

@@ -74,6 +74,11 @@ class TestGetStyle(NewFile):
         obj.BIMMaterialProperties.ifc_style_id = style.id()
         assert subject.get_style(obj) == style
 
+    def test_getting_nothing_for_a_broken_link_style(self):
+        obj = bpy.data.materials.new("Material")
+        obj.BIMMaterialProperties.ifc_style_id = 1
+        assert subject.get_style(obj) == None
+
 
 class TestGetSurfaceRenderingAttributes(NewFile):
     def test_get_colours_from_a_basic_material(self):