fix - function call with no args when using anthropic api

[ananis25]

When the arguments string is empty, replace it with an empty json dict, so pydantic can parse it correctly.

Fixes #407

[jackmpcollins]

Thank you!

---

Confirmed that Anthropic outputs an empty string in this case with

# Anthropic Raw Response

import anthropic

client = anthropic.Anthropic()

with client.messages.stream(
    max_tokens=1024,
    messages=[
        {
          "role": "user",
          "content": "Use the function to generate a random number. It takes no inputs and returns a random number."
        }
    ],
    model="claude-3-5-sonnet-20240620",
    tools=[
        {
          "name": "get_random_number",
          "description": "Get a random number",
          "input_schema": {
            "type": "object",
            "properties": {},
          }
        }
    ],
    # tool_choice={"type": "any"},
) as stream:
  for text in stream:
      print(text, flush=True)

outputting

RawMessageStartEvent(message=Message(id='msg_012K6zWDkhzPoJGpHoXv4EVy', content=[], model='claude-3-5-sonnet-20240620', role='assistant', stop_reason=None, stop_sequence=None, type='message', usage=Usage(cache_creation_input_tokens=0, cache_read_input_tokens=0, input_tokens=360, output_tokens=5)), type='message_start')
RawContentBlockStartEvent(content_block=TextBlock(text='', type='text'), index=0, type='content_block_start')
RawContentBlockDeltaEvent(delta=TextDelta(text="Certainly! I'll", type='text_delta'), index=0, type='content_block_delta')
TextEvent(type='text', text="Certainly! I'll", snapshot="Certainly! I'll")
RawContentBlockDeltaEvent(delta=TextDelta(text=' use the available function to generate a random number for you. This', type='text_delta'), index=0, type='content_block_delta')
TextEvent(type='text', text=' use the available function to generate a random number for you. This', snapshot="Certainly! I'll use the available function to generate a random number for you. This")
RawContentBlockDeltaEvent(delta=TextDelta(text=" function doesn't require any input parameters, so we can", type='text_delta'), index=0, type='content_block_delta')
TextEvent(type='text', text=" function doesn't require any input parameters, so we can", snapshot="Certainly! I'll use the available function to generate a random number for you. This function doesn't require any input parameters, so we can")
RawContentBlockDeltaEvent(delta=TextDelta(text=' call it directly.', type='text_delta'), index=0, type='content_block_delta')
TextEvent(type='text', text=' call it directly.', snapshot="Certainly! I'll use the available function to generate a random number for you. This function doesn't require any input parameters, so we can call it directly.")
ContentBlockStopEvent(index=0, type='content_block_stop', content_block=TextBlock(text="Certainly! I'll use the available function to generate a random number for you. This function doesn't require any input parameters, so we can call it directly.", type='text'))
RawContentBlockStartEvent(content_block=ToolUseBlock(id='toolu_01B481ftxp9FRP7CRA3EgbPv', input={}, name='get_random_number', type='tool_use'), index=1, type='content_block_start')
RawContentBlockDeltaEvent(delta=InputJSONDelta(partial_json='', type='input_json_delta'), index=1, type='content_block_delta')
InputJsonEvent(type='input_json', partial_json='', snapshot={})
ContentBlockStopEvent(index=1, type='content_block_stop', content_block=ToolUseBlock(id='toolu_01B481ftxp9FRP7CRA3EgbPv', input={}, name='get_random_number', type='tool_use'))
RawMessageDeltaEvent(delta=Delta(stop_reason='tool_use', stop_sequence=None), type='message_delta', usage=MessageDeltaUsage(output_tokens=72))
MessageStopEvent(type='message_stop', message=Message(id='msg_012K6zWDkhzPoJGpHoXv4EVy', content=[TextBlock(text="Certainly! I'll use the available function to generate a random number for you. This function doesn't require any input parameters, so we can call it directly.", type='text'), ToolUseBlock(id='toolu_01B481ftxp9FRP7CRA3EgbPv', input={}, name='get_random_number', type='tool_use')], model='claude-3-5-sonnet-20240620', role='assistant', stop_reason='tool_use', stop_sequence=None, type='message', usage=Usage(cache_creation_input_tokens=0, cache_read_input_tokens=0, input_tokens=360, output_tokens=72)))