[server] accept requests where 'content' is missing entirely, not just null or empty

[andysalerno]

I have encountered a problem very similar to #13471 .

That issue was fixed by allowing null or empty value for "content".

But my scenario (using pydantic-ai as a client) has requests where "content" is completely absent, in scenarios where there is a tool request.

If you look at the code for "at()" in json.hpp, you'll see it throws if the property is missing entirely.

This PR change fixed the issue for me locally.

Edit - here is an example of a message within a chat completions requests that has no content:

    {
      "role": "assistant",
      "tool_calls": [
        {
          "id": "qdAlNVrVB7fYP10SidYiSKx9MMbJCIb7",
          "type": "function",
          "function": {
            "name": "search_web",
            "arguments": "{\"query\":\"What is llama.cpp?\"}"
          }
        }
      ]
    }

looks related to #13516

[CISC]

Looks good, but can you also check if google/minja#63 needs to be applied to fix this completely?

[ngxson]

I think we should check if message contains either content OR tool_calls

[pwilkin]

@ngxson I think it's even more finegrained: only assistant role messages can contain either content or tool_calls. System, user and tool role messages have to contain content.

[pwilkin]

Per @ngxson comment ahove, added a pull request that checks for all the missing elements and produces meaningful error messages.

[pwilkin]

Also @CISC , tested on my case and tool calling seems to work properly now, doesn't seem that integrating the minja fix is required.

[CISC]

Superceded by #13540