BerriAI/litellm · error · ValueError

model must be a non-empty string

Error message

model must be a non-empty string

What it means

Pydantic field validator on the 'model' field of the fallback request model: it fires when model is empty or blank, i.e. the caller never specified which model the fallbacks attach to. Supply a non-empty model name.

Source

Thrown at litellm/types/management_endpoints/router_settings_endpoints.py:38

    fallback_type: Literal["general", "context_window", "content_policy"] = Field(
        default="general",
        description="Type of fallback: 'general' (default), 'context_window', or 'content_policy'",
    )

    @field_validator("fallback_models")
    @classmethod
    def validate_fallback_models(cls, v: list[str]) -> list[str]:
        if not v:
            raise ValueError("fallback_models must contain at least one model")
        if len(v) != len(set(v)):
            raise ValueError("fallback_models must not contain duplicates")
        return v

    @field_validator("model")
    @classmethod
    def validate_model(cls, v: str) -> str:
        if not v or not v.strip():
            raise ValueError("model must be a non-empty string")
        return v.strip()


class FallbackResponse(BaseModel):
    """Response model for fallback operations"""

    model: str = Field(description="The model name")
    fallback_models: list[str] = Field(description="List of fallback model names")
    fallback_type: str = Field(description="Type of fallback")
    message: str = Field(description="Success message")


class FallbackGetResponse(BaseModel):
    """Response model for getting fallbacks"""

    model: str = Field(description="The model name")
    fallback_models: list[str] = Field(description="List of fallback model names")
    fallback_type: str = Field(description="Type of fallback")

View on GitHub (pinned to 77b7c6c40c)

Solutions

1. Pass a non-empty model string, e.g. 'gpt-4o'.
2. Trim whitespace before validation.

When it happens

Trigger: Thrown at litellm/types/management_endpoints/router_settings_endpoints.py:38 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of BerriAI/litellm@77b7c6c40c (2026-08-18). Data as JSON: /api/errors/09c5efbf042c81e9. Report an issue: GitHub.