fix(feature): avoid IndexError when parsing a dtype with a trailing dot

lamindb/models/feature.py

@@ -297,7 +297,7 @@ def parse_nested_brackets(dtype_str: str) -> dict[str, Any]:
         # No brackets - handle simple cases like "A" or "A.field"
         if "." in dtype_str:
             parts = dtype_str.split(".")
-            if len(parts) == 2 and parts[1][0].isupper():
+            if len(parts) == 2 and parts[1] != "" and parts[1][0].isupper():
                 # bionty.CellType
                 return {"registry": dtype_str, "filter_str": "", "field": ""}
             elif len(parts) == 3:

tests/core/test_feature_dtype.py

@@ -9,6 +9,7 @@
 from lamindb.models.feature import (
     parse_dtype,
     parse_filter_string,
+    parse_nested_brackets,
     resolve_relation_filters,
     serialize_dtype,
 )
@@ -123,6 +124,19 @@ def test_serialize_with_field_information():
 # -----------------------------------------------------------------------------
 
 
+def test_parse_nested_brackets_trailing_dot():
+    # a trailing dot used to raise `IndexError: string index out of range`
+    # because `parts[1][0]` was accessed on an empty second part
+    assert parse_nested_brackets("bionty.") == {
+        "registry": "bionty",
+        "filter_str": "",
+        "field": "",
+    }
+    # malformed dtype must surface as a clear ValidationError, not IndexError
+    with pytest.raises(ValidationError):
+        parse_dtype("cat[bionty.]")
+
+
 def test_simple_record_with_subtype_and_field():
     # Create a Record type to get its UID
     customer_type = ln.Record(name="Customer", is_type=True).save()