Fix index error for empty sortby parameter (#2185)

Author: francbartoli

pygeoapi/api/itemtypes.py

@@ -431,12 +431,12 @@ def get_collection_items(
         for s in sorts:
             prop = s
             order = '+'
-            if s[0] in ['+', '-']:
+            if s and s[0] in ['+', '-']:
                 order = s[0]
                 prop = s[1:]
 
             if prop not in p.fields.keys():
-                msg = 'bad sort property'
+                msg = 'bad sortby property'
                 return api.get_exception(
                     HTTPStatus.BAD_REQUEST, headers, request.format,
                     'InvalidParameterValue', msg)

tests/api/test_itemtypes.py

@@ -3,9 +3,11 @@
 # Authors: Tom Kralidis <[email protected]>
 #          John A Stevenson <[email protected]>
 #          Colin Blackburn <[email protected]>
+#          Francesco Bartoli <[email protected]>
 #
 # Copyright (c) 2025 Tom Kralidis
 # Copyright (c) 2022 John A Stevenson and Colin Blackburn
+# Copyright (c) 2025 Francesco Bartoli
 #
 # Permission is hereby granted, free of charge, to any person
 # obtaining a copy of this software and associated documentation
@@ -285,6 +287,13 @@ def test_get_collection_items(config, api_):
     assert links[4]['rel'] == 'next'
     assert links[5]['rel'] == 'collection'
 
+    req = mock_api_request({
+        'sortby': ''
+    })
+    rsp_headers, code, response = get_collection_items(api_, req, 'obs')
+
+    assert code == HTTPStatus.BAD_REQUEST
+
     req = mock_api_request({
         'sortby': 'bad-property',
         'stn_id': '35'