lrclib: skip tracks where both plainLyrics and syncedLyrics are null

[stefanvanburen]

lrclib occasionally returns records with instrumental: false but plainLyrics: null and syncedLyrics: null — tracks that simply have no lyrics stored yet. A concrete example is Daft Punk - Nightvision (id 249829): lrclib has the record but no lyrics text for it:

$ curl 'https://lrclib.net/api/get?artist_name=Daft+Punk&track_name=Nightvision&album_name=Discovery' | jq
{
  "id": 249829,
  "name": "Nightvision",
  "trackName": "Nightvision",
  "artistName": "Daft Punk",
  "albumName": "Discovery",
  "duration": 104.0,
  "instrumental": false,
  "plainLyrics": null,
  "syncedLyrics": null,
  "lyricsfile": null
}

Before this change, LRCLyrics.get_text() would return None (the value of self.plain) and LRCLib.fetch() would pass it straight to Lyrics(None, ...), causing an AttributeError in Lyrics._split_lines when it called None.splitlines().

Fix both layers:

• LRCLib.fetch: guard the Lyrics construction with if lyrics := item.get_text(...) so a null result is treated as "not found" and the backend continues searching other candidates.
• Lyrics._split_lines: add a defensive (self.text or "") guard so the dataclass does not crash if it is ever constructed with text=None through another code path.

Add a test case that exercises the null/null response path.

• Documentation.
• Changelog.
• Tests.

[github-actions]

Thank you for the PR! The changelog has not been updated, so here is a friendly reminder to check if you need to add an entry.

[Copilot]

Pull request overview

grug see PR try make lrclib backend not crash when API say instrumental=false but both lyrics fields null. goal good: treat that like “not found” and keep searching, plus add extra guard in Lyrics split.

Changes:

• LRCLib.fetch now skip building Lyrics(...) when item.get_text(...) return null-ish.
• Lyrics._split_lines now tolerate text=None by using empty string.
• Add pytest case for lrclib response where both plainLyrics and syncedLyrics are null.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
test/plugins/test_lyrics.py	add coverage for lrclib response with both lyrics fields null
beetsplug/lyrics.py	change LRCLib.fetch to skip null lyrics text
beets/util/lyrics.py	guard _split_lines against text=None

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.95%. Comparing base (7c90645) to head (e6be20e).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6767   +/-   ##
=======================================
  Coverage   74.95%   74.95%           
=======================================
  Files         163      163           
  Lines       20893    20893           
  Branches     3291     3292    +1     
=======================================
  Hits        15661    15661           
  Misses       4474     4474           
  Partials      758      758           

Files with missing lines	Coverage Δ
beets/util/lyrics.py	96.70% <ø> (ø)
beetsplug/lyrics.py	89.78% <100.00%> (ø)

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