BaseTool.additional_instructions parameter is mandatory

[bonk1t]

The issue is that we enforce strict str type on the additional_instructions parameter:

🐧 RoutingAgent 🛠️ Executing Function
Function(arguments='{"my_primary_instructions":"...","recipient":"...Agent","message":"...","additional_instructions":null}', name='SendMessage')
────────────────────────────────────────────────────────────────────────────────
SendMessage ⚙️ Function Output
Error: 1 validation error for SendMessage additional_instructions Input should
be a valid string [type=string_type, input_value=None, input_type=NoneType]

The fix: to use str | None