iflytek/astron-agent · error · RequestValidationError

'content' cannot be empty

Error message

'content' cannot be empty

What it means

validate_messages_params in core/agent's OpenAI-compatible schema layer raises a fastapi RequestValidationError when any message in the request's `messages` array has empty or missing `content`. It emits a per-item error at loc body.messages[i].content with msg "'content' cannot be empty", mirroring OpenAI API validation behavior.

Solutions

  1. Ensure every messages[i] includes a non-empty string `content` before sending.
  2. For assistant tool-call messages, set content to an empty-compatible value the API accepts only if the schema allows; otherwise omit such messages or add content text.
  3. Trim input: reject or coalesce whitespace-only strings to a default prompt client-side.
  4. Check the server response loc field (body.messages[i].content) to identify the offending index.

Example fix

# before
messages = [{"role": "user"}]

# after
messages = [{"role": "user", "content": "Hello"}]
Defensive patterns

Strategy: validation

Validate before calling

def validate_messages(messages):
    for i, m in enumerate(messages):
        if not isinstance(m, dict) or not m.get("content"):
            raise ValueError(f"messages[{i}].content must be non-empty")

Type guard

def has_content(m: dict) -> bool:
    return isinstance(m.get("content"), str) and bool(m["content"].strip())

Try / catch

import httpx
try:
    r = httpx.post(url, json=payload)
except httpx.HTTPStatusError as e:
    # 422 from RequestValidationError; inspect e.response.json()['detail']
    for err in e.response.json().get('detail', []):
        print(err['loc'], err['msg'])

Prevention

When it happens

Trigger: POSTing to the agent's chat/completions-style endpoint with a message dict lacking `content` (e.g. {"role":"user"}) or with content ""/null — including assistant messages that only carry tool_calls and no content.

Common situations: Client code appends a placeholder user message before filling content; assistant messages built from tool-call responses where content is None; upstream gateway strips content; hand-rolled request JSON missing the field.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

AI-assisted analysis of iflytek/astron-agent@5e758547a8 (2026-09-12). Data as JSON: /api/errors/a3d88baa86167d83. Report an issue: GitHub.

Appendix: source

Thrown at core/agent/api/schemas/base_inputs.py:43

    @model_validator(mode="before")  # type: ignore[misc]
    @classmethod
    def validate_messages_params(cls, values: Any) -> Any:
        if not isinstance(values, dict):
            return values
        messages = values.get("messages", [])
        if isinstance(messages, list) and not messages:
            values.pop("messages", None)
            return values

        next_role = "user"
        for i, message in enumerate(messages):
            if not isinstance(message, dict):
                return values

            if not message.get("content"):
                # Content cannot be empty
                raise RequestValidationError(
                    errors=[
                        {
                            "type": "literal_error",
                            "loc": ("body", "messages", i, "content"),
                            "msg": "'content' cannot be empty",
                        }
                    ]
                )

            if message.get("role") == "system":
                # System role not supported
                raise RequestValidationError(
                    errors=[
                        {
                            "type": "literal_error",
                            "loc": ("body", "messages", i, "role"),
                            "msg": "'role' must be user or assistant",
                        }

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