Use model key presence when resolving get defaults

ollama/_types.py

@@ -98,7 +98,7 @@ def get(self, key: str, default: Any = None) -> Any:
     >>> msg.get('tool_calls')[0]['function']['name']
     'foo'
     """
-    return getattr(self, key) if hasattr(self, key) else default
+    return getattr(self, key) if key in self else default
 
 
 class Options(SubscriptableBaseModel):

tests/test_type_mapping.py

@@ -0,0 +1,23 @@
+import pytest
+
+from ollama import Message, Tool
+
+
+@pytest.mark.parametrize('key', ['content', 'model_dump', 'nonexistent'])
+def test_get_missing_key_uses_default(key):
+  message = Message(role='assistant')
+  fallback = object()
+
+  with pytest.raises(KeyError):
+    message[key]
+  assert message.get(key, fallback) is fallback
+
+
+@pytest.mark.parametrize('content', [None, ''])
+def test_get_preserves_explicit_values(content):
+  message = Message(role='assistant', content=content)
+  assert message.get('content', 'fallback') == content
+
+
+def test_get_preserves_model_default():
+  assert Tool().get('type', 'fallback') == 'function'