Fix #3038. Fix #3039. Selector should default to none instead for throwing errors if the query doesn't have a result.

src/ifcopenshell-python/ifcopenshell/util/selector.py

@@ -255,6 +255,8 @@ class Selector:
         value = element
         for key in keys:
             key = key.strip()
+            if value is None:
+                return
             if key == "type":
                 value = ifcopenshell.util.element.get_type(value)
             elif key in ("material", "mat"):
@@ -302,7 +304,10 @@ class Selector:
                     value = value.get(key, None)
             elif isinstance(value, (list, tuple)): # If we use regex
                 if key.isnumeric():
-                    value = value[int(key)]
+                    try:
+                        value = value[int(key)]
+                    except IndexError:
+                        return
                 else:
                     results = []
                     for v in value:

src/ifcopenshell-python/test/util/test_selector.py

@@ -56,6 +56,23 @@ class TestGetElementValue(test.bootstrap.IFC4):
         # Provide shortform for convenience
         assert subject.get_element_value(element, "mat.i.Name") == ["L1", "L2"]
 
+    def test_selecting_a_query_that_fails_silently(self):
+        element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
+        assert subject.get_element_value(element, "material.item.Name.0") is None
+
+    def test_selceting_a_list_item_that_fails_silently(self):
+        element = ifcopenshell.api.run("root.create_entity", self.file, ifc_class="IfcWall")
+        material = ifcopenshell.api.run("material.add_material", self.file, name="CON01")
+        material2 = ifcopenshell.api.run("material.add_material", self.file, name="CON02")
+        material_set = ifcopenshell.api.run(
+            "material.add_material_set", self.file, name="FOO", set_type="IfcMaterialLayerSet"
+        )
+        layer = ifcopenshell.api.run("material.add_layer", self.file, layer_set=material_set, material=material)
+        layer.Name = "L1"
+        ifcopenshell.api.run("material.assign_material", self.file, product=element, material=material_set)
+        assert subject.get_element_value(element, "material.item.Name.0") == "L1"
+        assert subject.get_element_value(element, "material.item.Name.1") is None
+
 
 class TestSelector(test.bootstrap.IFC4):
     def test_selecting_by_class(self):