[davrens101]

Bug

_copy_messages() dropped every falsy field (if v), so a chat message
built with empty content (e.g. [{'role': 'user', 'content': ''}]) was
sent with content unset (None). Only unset None values should be
omitted — downstream serialization already drops None via
model_dump(exclude_none=True).

Reproduction (CPU, no server)

import sys
sys.path.insert(0, 'ollama-python')
from ollama._client import _copy_messages

msgs = list(_copy_messages([{'role': 'user', 'content': ''}]))
print(msgs[0].content, msgs[0].model_fields_set)

Before: content=None, fields_set={'role'} (empty content lost)
After: content='', fields_set={'content', 'role'}

Fix

ollama/_client.py: change if v to if v is not None in _copy_messages
so falsy-but-set values (empty content, etc.) are preserved while unset
None values are still dropped.

Validation

• Regression test added: tests/test_utils.py::test_copy_messages_preserves_empty_content
• pytest tests/test_utils.py -> 11 passed
• The 2 failures in tests/test_type_serialization.py are pre-existing and
  unrelated (Windows tempfile locking / image path handling,
  Tests fail on Windows due to NamedTemporaryFile locking behavior #676)

Before / After

	Before	After
content='' message	content=None (lost)	content='' (preserved)

AI-assisted contribution. Reproduced on unmodified code, then fixed.