diff --git a/pydynamodb/__init__.py b/pydynamodb/__init__.py
index ebc1cf1..363b37f 100644
--- a/pydynamodb/__init__.py
+++ b/pydynamodb/__init__.py
@@ -6,7 +6,7 @@
 if TYPE_CHECKING:
     from .connection import Connection
 
-__version__: str = "0.6.2"
+__version__: str = "0.6.3"
 
 # Globals https://www.python.org/dev/peps/pep-0249/#globals
 apilevel: str = "2.0"
diff --git a/pydynamodb/converter.py b/pydynamodb/converter.py
index 0959cf9..ff0b00d 100644
--- a/pydynamodb/converter.py
+++ b/pydynamodb/converter.py
@@ -220,7 +220,7 @@ def _to_list(self, value: Optional[List[Any]], **kwargs) -> Optional[List[Any]]:
         return coverted_
 
     def _to_null(self, value: Optional[bool], **kwargs) -> Optional[bool]:
-        return value
+        return None
 
     def _to_bool(self, value: Optional[bool], **kwargs) -> Optional[bool]:
         return value
diff --git a/tests/test_converter.py b/tests/test_converter.py
index eedb4c9..8b19496 100644
--- a/tests/test_converter.py
+++ b/tests/test_converter.py
@@ -243,7 +243,8 @@ def test_deserializer_map(self, converter):
         }
 
     def test_deserializer_null(self, converter):
-        assert converter.deserialize({"NULL": True})
+        assert converter.deserialize({"NULL": True}) is None
+        assert converter.deserialize({"NULL": False}) is None
 
     def test_deserializer_bool(self, converter):
         assert converter.deserialize({"BOOL": True})
diff --git a/tests/test_superset_dml_select.py b/tests/test_superset_dml_select.py
index 7f9d1e2..2f97cc8 100644
--- a/tests/test_superset_dml_select.py
+++ b/tests/test_superset_dml_select.py
@@ -127,3 +127,24 @@ def test_parse_nested_select_case_4(self):
             "Statement": "SELECT col_str,col_datetime,col_num "
             + "FROM \"Issues\" WHERE key_partition = 'row_1'"
         }
+
+    def test_parse_nested_select_case_4(self):
+        sql = """
+        SELECT text_split(id,'.',1) FROM (
+            SELECT id FROM "lakefront-ingest-stg-config-table"
+        )
+        """
+        parser = SQLParser(sql, parser_class=SupersetSelect)
+        ret = parser.transform()
+
+    def test_parse_nested_select_case_5(self):
+        sql = """
+        SELECT id FROM (
+            SELECT text_split(id,'.',1) FROM (
+                SELECT id FROM "lakefront-ingest-stg-config-table"
+            )
+        ) AS virtual_table
+        GROUP BY id
+        """
+        parser = SQLParser(sql, parser_class=SupersetSelect)
+        ret = parser.transform()
\ No newline at end of file