[FIX] Handle empty local nodes file (#67)

* fix handling of empty nodes JSON and add test

* move test case for empty dict to schema invalid test

app/api/utility.py

@@ -55,6 +55,8 @@ def parse_nodes_as_dict(path: Path) -> dict:
     where the keys are the node URLs, and the values are the node names.
     Makes sure node URLs end with a slash and only valid nodes are returned.
     """
+    valid_nodes = []
+
     if path.exists() and path.stat().st_size > 0:
         try:
             with open(path, "r") as f:
@@ -75,7 +77,6 @@ def parse_nodes_as_dict(path: Path) -> dict:
             validate(instance=input_nodes, schema=LOCAL_NODE_SCHEMA)
             valid_nodes = input_nodes
         except jsonschema.ValidationError:
-            valid_nodes = []
             invalid_nodes = []
             for node in input_nodes:
                 try:

tests/test_utility.py

@@ -56,7 +56,6 @@ def test_add_trailing_slash(url, expected_url):
                 "https://secondnode.neurobagel.org/query/": "secondnode",
             },
         ),
-        ({}, {}),
     ],
 )
 def test_parse_nodes_as_dict(set_nodes, expected_nodes, tmp_path):
@@ -190,6 +189,7 @@ def test_validate_query_node_url_list(
                 "https://firstnode.neurobagel.org/query/": "firstnode",
             },
         ),
+        ({}, {}),
     ],
 )
 def test_schema_invalid_nodes_raise_warning(
@@ -220,3 +220,12 @@ def test_invalid_json_raises_warning(tmp_path):
 
     with pytest.warns(UserWarning, match="You provided an invalid JSON"):
         util.parse_nodes_as_dict(tmp_path / "local_nb_nodes.json")
+
+
+def test_empty_json_does_not_error(tmp_path):
+    """Ensure that an empty JSON file does not raise an error."""
+
+    with open(tmp_path / "local_nb_nodes.json", "w") as f:
+        f.write("")
+
+    assert util.parse_nodes_as_dict(tmp_path / "local_nb_nodes.json") == {}