500 Internal Server Error on category search with zero matching results

[Itz-Agasta]

Describe the bug
Any /search request using the hidden [key=value] category syntax combined with a free-text near-phrase crashes with an uncaught IndexError, returned to the client as a generic 500 Internal Server Error, whenever the category search legitimately returns zero results.

Basically thr ForwardGeocoder.sort_and_cut_results() in src/nominatim_api/search/geocoder.py unconditionally indexes results[0]:

def sort_and_cut_results(self, results: SearchResults) -> SearchResults:
    results.sort(key=lambda r: (r.ranking, 0 if r.bbox is None else -r.bbox.area))
    final = SearchResults()
    min_rank = results[0].rank_search   # IndexError if results is empty
    min_ranking = results[0].ranking
    ...

git blame shows the guard against empty results was removed in commit 87a8c24 ("improve result cutting when a POI comes out with top importance", 2025-06-01), which previously wrapped this block in if results:. Still present and unfixed on current master (2991c61).

This is confirmed independent of any specific category backend (old class/type place_classtype_* tables or the newer ltree-based categories column) -- it reproduces on production, which uses the old mechanism.

To Reproduce

curl -G "https://nominatim.openstreetmap.org/search" \
  --data-urlencode "q=[amenity=xyzxyz] Berlin" \
  --data-urlencode "format=json"

Response: {"title": "500 Internal Server Error"} (HTTP 500). amenity=xyzxyz is not a real OSM tag value, so this query is guaranteed zero category matches everywhere, ruling out a data/import-specific cause.

Software Environment (please complete the following information):

• Nominatim version: 5.3.99-2 (current master, commit 2991c61)
• Postgresql version: 17.9 (Debian 17.9-0+deb13u1)
• Postgis version: 3.5.2
• OS: Debian (x86_64-pc-linux-gnu

Hardware Configuration (please complete the following information):

• RAM:
• number of CPUs:
• type and size of disks:

Ahhh i cant recall

Postgresql Configuration:

NIL

Nominatim Configuration:

NIL

Additional context

Confirmed on two independent instances:

• nominatim.openstreetmap.org (production) -- [amenity=xyzxyz] Berlin -> HTTP 500
• our planet test instance -- same guaranteed-zero-match category, and the originally-noticed [club=scout] Vaduz -> HTTP 500

[Itz-Agasta]

Also reproduced directly via the Python API with a full traceback:

import nominatim_api as napi
api = napi.NominatimAPI(...)
api.search_category([('amenity', 'xyzxyz')], near_query='Berlin')
Traceback (most recent call last):
  File ".../nominatim_api/core.py", line 364, in search_category
    return await geocoder.lookup_pois(categories, phrases)
  File ".../nominatim_api/search/geocoder.py", line 280, in lookup_pois
    results = self.sort_and_cut_results(results)
  File ".../nominatim_api/search/geocoder.py", line 181, in sort_and_cut_results
    min_rank = results[0].rank_search
IndexError: list index out of range

[mtmail]

Can you also reproduce this in the CLI? I don't see the error but maybe the CLI parses it slightly different.

nominatim search --query "[amenity=xyzxyz] Andorra" --format debug

#### Debug output for forward_lookup() Parameters: phrases: [Phrase(ptype=0, text='[amenity=xyzxyz] Andorra')] params: SearchDetails(geometry_output=<GeometryFormat.NONE: 0>, address_details=True, linked_places=False, parented_places=False, keywords=False, geometry_simplification=0.0, locales=<nominatim_api.localization.Locales object at 0xfef1cbd72ff0>, max_results=20, min_rank=0, max_rank=30, layers=None, countries=[], excluded=[], viewbox=None, bounded_viewbox=False, near=None, near_radius=None, categories=[], viewbox_x2=None) [2026-07-09 15:14:42.146678] # Analyze query (using ICU tokenizer) Normalized query: [Phrase(ptype=0, text='amenity-xyzxyz andorra')] Transliterated query: <amenity-xyzxyz andorra>

[Itz-Agasta]

yes y can't reproduce it via the CLI because the CLI never parses [key=value] bracket syntax at all -- that only happens in the HTTP /search endpoint. To reproduce, hit the HTTP API directly:

curl "https://nominatim.openstreetmap.org/search?q=%5Bamenity%3Dxyzxyz%5D%20Andorra&format=json"

I just ran this and got a 500 both on the public production server and on my own test server. So it's reproducible right now on stock production Nominatim.