Guard _fetch_sec_filings and _fetch_calendar against null/empty Yahoo results

[8910work-cell]

Problem

_fetch_sec_filings runs filings = result["quoteSummary"]["result"][0]["secFilings"]["filings"] immediately after the if result is None: return None guard. When Yahoo returns a non-None payload whose quoteSummary.result is null/empty (or is missing the secFilings key), this crashes with TypeError: 'NoneType' object is not subscriptable (or KeyError/IndexError).

_fetch_calendar has the same class of gap: its parse block only catches (KeyError, IndexError), so a null nested structure raises an uncaught TypeError.

Fix

• _fetch_sec_filings: wrap the nested lookup in try/except (KeyError, IndexError, TypeError) and return None — graceful degradation, consistent with the existing result is None guard.
• _fetch_calendar: add TypeError to the existing except tuple.

Tests

Adds network-free regression tests (mocking Quote._fetch) in tests/test_ticker.py:

• test_sec_filings_null_result — a null result degrades to None instead of crashing
• test_sec_filings_happy_path — a valid payload still parses correctly
• test_calendar_null_result — a null result raises a clean YFDataException

Verified red→green: test_sec_filings_null_result fails on current dev with TypeError: 'NoneType' object is not subscriptable and passes with this change.

[ValueRaider]

When does Yahoo returns a non-None payload?

[8910work-cell]

Good question. _fetch() returns the parsed JSON whenever the HTTP request itself succeeds — it only returns None on an HTTPError (with hide_exceptions). So the existing if result is None guard at the top of both methods catches a failed request, not a successful HTTP 200 whose body has quoteSummary.result: null.

Yahoo returns that shape for symbols/modules it has no data for (delisted or invalid tickers, region-restricted symbols, or a module that simply returns nothing):

{"quoteSummary": {"result": null, "error": null}}

result["quoteSummary"]["result"] is then None, and [0] raises TypeError: 'NoneType' object is not subscriptable. It's the same "Yahoo returns an empty payload" class already fixed for the sibling methods in #2863 and #2877, and reported for _fetch_info in #2865.

Reproduced on current dev (f9eb690), network-free:

from unittest.mock import patch, MagicMock
from yfinance.scrapers.quote import Quote

null_payload = {"quoteSummary": {"result": None, "error": None}}
for name in ("_fetch_sec_filings", "_fetch_calendar"):
    q = Quote(MagicMock(), "DELISTED")
    with patch.object(Quote, "_fetch", return_value=null_payload):
        getattr(q, name)()
# _fetch_sec_filings -> TypeError: 'NoneType' object is not subscriptable
# _fetch_calendar    -> TypeError: 'NoneType' object is not subscriptable

Note _fetch_calendar already caught (KeyError, IndexError) — the []/missing-key cases — so this PR only adds the TypeError that the None case raises; _fetch_sec_filings had no guard at all. After the change _fetch_sec_filings returns None and _fetch_calendar raises YFDataException (its existing error path), matching how sustainability / recommendations / upgrades_downgrades already handle the same access chain.

[ValueRaider]

My point was - I prefer checking for specific values instead of exception. Maybe when that keyerror happens, there is another key with information.

Also I expect to speak with a human not a bot.