from typing import Optional


def doc_to_doc_string(doc: Optional[str], indent_level: int = 0) -> str:
    """Generate a documentation string from a schema salad doc field."""
    lead = " " + "  " * indent_level + "* "
    if doc:
        doc_str = "\n".join([f"{lead}{line}" for line in doc.split("\n")])
    else:
        doc_str = ""
    return doc_str