fix: override_if_not_empty should not skip falsy primitives (0, False, 0.0)

deepmerge/strategy/type_conflict.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+from collections.abc import Sized
 from typing import Any, TypeVar
 
 import deepmerge.merger
@@ -30,5 +31,14 @@ def strategy_use_existing(
     def strategy_override_if_not_empty(
         config: deepmerge.merger.Merger, path: list, base: T1, nxt: T2
     ) -> T1 | T2:
-        """overrides the new object over the old object only if the new object is not empty or null"""
-        return nxt if nxt else base
+        """overrides the new object over the old object only if the new object is not empty or null.
+
+        ``None`` is treated as null.  Sized objects (``dict``, ``list``, ``set``, ``str``, …) are
+        treated as empty when ``len(nxt) == 0``.  All other values — including falsy primitives such
+        as ``0``, ``0.0``, and ``False`` — are considered non-empty and will override *base*.
+        """
+        if nxt is None:
+            return base
+        if isinstance(nxt, Sized) and len(nxt) == 0:
+            return base
+        return nxt

deepmerge/tests/strategy/test_type_conflict.py

@@ -20,3 +20,15 @@ def test_merge_if_not_empty():
 
     strategy = TypeConflictStrategies.strategy_override_if_not_empty({}, [], CONTENT_AS_LIST, None)
     assert strategy == CONTENT_AS_LIST
+
+
+def test_merge_if_not_empty_falsy_primitives():
+    """Falsy primitives (0, False) are valid non-empty values and should override base."""
+    strategy = TypeConflictStrategies.strategy_override_if_not_empty({}, [], "base", 0)
+    assert strategy == 0, "integer zero is not empty; it should override base"
+
+    strategy = TypeConflictStrategies.strategy_override_if_not_empty({}, [], "base", False)
+    assert strategy is False, "False is not empty; it should override base"
+
+    strategy = TypeConflictStrategies.strategy_override_if_not_empty({}, [], "base", 0.0)
+    assert strategy == 0.0, "0.0 is not empty; it should override base"