Make an empty DiffSync instance evaluate to True.

Author: Leo Kirchner

.flake8

@@ -2,3 +2,4 @@
 # E501: Line length is enforced by Black, so flake8 doesn't need to check it
 # W503: Black disagrees with this rule, as does PEP 8; Black wins
 ignore = E501, W503
+exclude = .venv

diffsync/__init__.py

@@ -459,6 +459,13 @@ def __str__(self) -> StrType:
     def __repr__(self) -> StrType:
         return f"<{str(self)}>"
 
+    def __bool__(self) -> bool:
+        """Always evaluate DiffSync instances as True.
+
+        This is needed because without it the __len__ method would be used, which in turn would cause empty DiffSync
+        instances to evaluate as False."""
+        return True
+
     def __len__(self) -> int:
         """Total number of elements stored."""
         return self.store.count()

tests/unit/test_diffsync.py

@@ -992,6 +992,10 @@ class NoDeleteInterfaceDiffSync(BackendA):
     assert not diff.has_diffs()
 
 
+def test_diffsync_empty_instance_is_truthy():
+    assert bool(Adapter())
+
+
 def test_diffsync_tree_traversal():
     assert BackendA.get_tree_traversal(True) == {"site": {"device": {"interface": {}}, "person": {}}, "unused": {}}
     text = """\