fix: LRUCache.get() and __getitem__() fail for cached None values

[koteshyelamati]

Problem

LRUCache.get() and LRUCache.__getitem__() both break when None is a legitimate cached value.

get() bug: uses if value is not None: to detect cache hits, so if a key maps to None, it skips the LRU promotion and returns the default instead of the cached None.

__getitem__() bug: calls self.get(key) and then checks if value is None: raise KeyError, so it raises KeyError even when the key exists with value None.

cache = LRUCache(capacity=5)
cache['key'] = None

cache.get('key', 'missing')  # Returns 'missing' instead of None
cache['key']                  # Raises KeyError instead of returning None

Root cause

Both methods use the cached value itself as a sentinel to detect cache misses. This is the same class of bug that was fixed in set() by PR #597.

Fix

Replace the value-based checks with key not in self.cache membership tests, consistent with how set() was already fixed.

[msiemens]

Thanks for the PR, @koteshyelamati! Could you add one or two tests for this?

[uadhran]

Confirmed this still reproduces on current master (4aa5311, TinyDB 4.9.0) — not fixed by the recent docs/type PRs.

from tinydb.utils import LRUCache

c = LRUCache(capacity=5)
c['k'] = None

assert 'k' in c.cache          # key is present
print(c.get('k', 'missing'))   # 'missing'  (expected None)
# c['k'] → KeyError            (expected None)

Root cause matches the PR: get() / __getitem__() still use is not None as a hit check (tinydb/utils.py), while set() already uses membership (key in self.cache) after #596/#597.

Also worth noting: docs/changelog.rst currently says falsy values like 0 or None are handled correctly in LRUCache, but get/__getitem__ for stored None still fail — so this PR would also align the changelog claim with behavior.

Suggested tests (if helpful)

Happy to help with tests if useful — something like:

def test_lru_cache_none_value():
    cache = LRUCache(capacity=3)
    cache['key'] = None

    assert 'key' in cache.cache
    assert cache.get('key', 'missing') is None
    assert cache['key'] is None

    # LRU promotion still works for None hits
    cache['a'] = 1
    cache['b'] = 2
    cache.get('key')   # touch
    cache['c'] = 3     # would evict oldest if 'key' wasn't promoted
    assert cache.get('key') is None

(I don’t want to step on this PR — just adding verification + test ideas.)