From edef5aceac02f97f98663fe6eb812df467c0dc53 Mon Sep 17 00:00:00 2001
From: dsgibbons <dsgibbons@tuta.io>
Date: Thu, 17 Oct 2024 07:32:38 +1030
Subject: [PATCH] fix: empty list validation

---
 src/patito/validators.py |  2 ++
 tests/test_validators.py | 29 +++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/src/patito/validators.py b/src/patito/validators.py
index 7112898..399ddea 100644
--- a/src/patito/validators.py
+++ b/src/patito/validators.py
@@ -175,6 +175,8 @@ def _find_errors(  # noqa: C901
             .select(column)
             # Remove those rows that do not contain lists at all
             .filter(pl.col(column).is_not_null())
+            # Remove empty lists
+            .filter(pl.col(column).list.len() > 0)
             # Convert lists of N items to N individual rows
             .explode(column)
             # Calculate how many nulls are present in lists
diff --git a/tests/test_validators.py b/tests/test_validators.py
index b534199..7c1dbf0 100644
--- a/tests/test_validators.py
+++ b/tests/test_validators.py
@@ -637,6 +637,35 @@ class NestedPositiveStructModel(pt.Model):
         NestedPositiveStructModel.validate(bad_df)
 
 
+def test_empty_list_validation() -> None:
+    """Test validation of model with empty lists."""
+
+    class TestModel(pt.Model):
+        list_field: list[str]
+
+    # validate presence of an empty list
+    df = pl.DataFrame({"list_field": [["a", "b"], []]})
+    TestModel.validate(df)
+
+    # validate when all lists are empty, so long as the schema is correct
+    df = pl.DataFrame(
+        {"list_field": [[], []]}, schema={"list_field": pl.List(pl.String)}
+    )
+    TestModel.validate(df)
+
+    class NestedTestModel(pt.Model):
+        nested_list_field: list[list[str]]
+
+    df = pl.DataFrame({"nested_list_field": [[["a", "b"], ["c"]], []]})
+    NestedTestModel.validate(df)
+
+    df = pl.DataFrame(
+        {"nested_list_field": [[], []]},
+        schema={"nested_list_field": pl.List(pl.List(pl.String))},
+    )
+    NestedTestModel.validate(df)
+
+
 def test_list_struct_validation() -> None:
     """Test validation of model with list of structs column."""