diff --git a/quinn/schema_helpers.py b/quinn/schema_helpers.py
index 8fd18b1a..d314ff1b 100644
--- a/quinn/schema_helpers.py
+++ b/quinn/schema_helpers.py
@@ -132,7 +132,7 @@ def _lookup_type(type_str: str) -> T.DataType:
 
         return type_lookup[type_str]
 
-    def _convert_nullable(null_str: str) -> bool:
+    def _convert_nullable(null_str: Optional[str]) -> bool:
         if null_str is None:
             return True
 
@@ -159,8 +159,8 @@ def _convert_nullable(null_str: str) -> bool:
         field = T.StructField(
             name=row["name"],
             dataType=_lookup_type(row["type"]),
-            nullable=_convert_nullable(row.get("nullable", True)),
-            metadata=_validate_json(row.get("metadata", None)),
+            nullable=_convert_nullable(row["nullable"]) if "nullable" in row else True,
+            metadata=_validate_json(row["metadata"] if "metadata" in row else None),  # noqa: SIM401
         )
         fields.append(field)
 
@@ -175,4 +175,8 @@ def complex_fields(schema: T.StructType) -> dict[str, object]:
     :return: A dictionary with complex field names as keys and their respective data types as values.
     :rtype: Dict[str, object]
     """
-    return {field.name: field.dataType for field in schema.fields if isinstance(field.dataType, (T.ArrayType, T.StructType, T.MapType))}
+    return {
+        field.name: field.dataType
+        for field in schema.fields
+        if isinstance(field.dataType, (T.ArrayType, T.StructType, T.MapType))
+    }