[Bug] Ollama json.loads empty tool arguments abort request assembly

Description

Ollama request assembly calls json.loads on tool-call arguments whenever they are a string. Empty strings and invalid JSON raise JSONDecodeError and abort the request. None is passed through as None instead of {}.

Steps to Reproduce

from agno.models.message import Message
from agno.models.ollama.chat import Ollama

model = Ollama()
assistant = Message(
    role="assistant",
    content=None,
    tool_calls=[{
        "id": "call_1",
        "type": "function",
        "function": {"name": "get_weather", "arguments": ""},
    }],
)
model._format_message(assistant)

Expected Behavior

Empty, null, or invalid JSON arguments become {}. A dict is passed through. Request assembly succeeds.

Actual Behavior

json.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

Environment

• OS: Windows 11
• Agno Version: current main
• Additional Environment Details: Python 3.13

Possible Solutions (optional)

Parse string arguments with a try/except. Treat None or blank strings as {}. Pass dicts through.