[liugedragon]

With fuzzFactor: 1, replacing a context line with x works, but replacing it with an empty line can make the same patch fail. An extra empty context line has the same problem.

The matcher uses a truthiness check before trying context substitutions and insertions. An empty string is a valid file line, so use an explicit non-null check, as the deletion branch already does. End-of-file handling and exact matching remain unchanged.

Nine regression tests cover substitutions and insertions with LF, CRLF, and automatic CRLF-to-LF conversion, plus strict matching, missing EOF context, and required deletion lines. On unchanged upstream, four fail and five controls pass; all nine pass with this change.

Validation:

• Ubuntu 22.04 / Node 22.18.0 / Yarn 4.18.1: yarn install --immutable and the complete yarn test passed: 327 tests, including lint, build, type checks, bundles, and coverage.
• Windows: complete build and 196 patch tests passed.
• A bounded 60,000-case comparison against the unchanged matcher with blank source lines encoded as ordinary nonempty tokens agreed throughout; 945 previously rejected cases now apply. Original context lines were unique and nonempty, with one source edit and fuzz budgets 0–2.
• git diff --check: passed.

The fuzzy-search memoization work in #711 and #716 retains the condition fixed here.