def is_truthy(val) -> bool:
    return str(val).lower() in ('1', 'true', 'yes', 'on')

def normalize_fields_param(params: dict | None) -> list[str]:
    if not params:
        return []
    raw = params.get("fields")
    if isinstance(raw, (list, tuple)):
        out: list[str] = []
        for item in raw:
            if isinstance(item, str):
                out.extend([p for p in (s.strip() for s in item.split(",")) if p])
        return out
    if isinstance(raw, str):
        return [p for p in (s.strip() for s in raw.split(",")) if p]
    return []