Fix #166 (#193)

nornir/core/inventory.py

@@ -304,11 +304,23 @@ def __init__(
 
         self.defaults = defaults or {}
 
-        self.groups = groups or {}
-        for n, g in self.groups.items():
-            if isinstance(g, dict):
-                g = Group(name=n, nornir=nornir, **g)
-            self.groups[n] = g
+        self.groups: Dict[str, Group] = {}
+        if groups is not None:
+            for group_name, group_details in groups.items():
+                if group_details is None:
+                    group = Group(name=group_name, nornir=nornir)
+                elif isinstance(group_details, dict):
+                    group = Group(name=group_name, nornir=nornir, **group_details)
+                elif isinstance(group_details, Group):
+                    group = group_details
+                else:
+                    raise ValueError(
+                        f"Parsing group {group_name}: "
+                        f"expected dict or Group object, "
+                        f"got {type(group_details)} instead"
+                    )
+
+                self.groups[group_name] = group
 
         for group in self.groups.values():
             group.groups = self._resolve_groups(group.groups)

tests/core/test_inventory.py

@@ -246,6 +246,7 @@ def test_to_dict(self):
                     "groups": ["parent_group"],
                 },
                 "group_2": {"name": "group_2", "site": "site2"},
+                "empty_group": {"name": "empty_group"},
             },
         }
         assert inventory.filter(role="www").to_dict() == expected

tests/inventory_data/groups.yaml

@@ -17,3 +17,5 @@ group_1:
 
 group_2:
     site: site2
+
+empty_group: