refactor: removed nullable in models

models/mixins.py

@@ -9,17 +9,13 @@ class IdMixin:
 
 
 class SoftDeleteMixin:
-    is_deleted: Mapped[bool] = mapped_column(
-        default=False,
-        nullable=False,
-    )
+    is_deleted: Mapped[bool] = mapped_column(default=False)
 
 
 class CreatedAtMixin:
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True),
         default=lambda: datetime.now(timezone.utc),
-        nullable=False,
     )
 
 
@@ -27,7 +23,6 @@ class LastModifiedAtMixin:
     last_modified_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True),
         default=lambda: datetime.now(timezone.utc),
-        nullable=False,
     )