fix bug when user enters an empty string (#992)

Author: dantownsend

piccolo/apps/migrations/commands/backwards.py

@@ -78,9 +78,11 @@ async def run_migrations_backwards(self, app_config: AppConfig):
         _continue = (
             "y"
             if self.auto_agree
-            else input(f"Reverse {n} migration{'s' if n != 1 else ''}? [y/N] ")
+            else input(
+                f"Reverse {n} migration{'s' if n != 1 else ''}? [y/N] "
+            ).lower()
         )
-        if _continue in "yY":
+        if _continue == "y":
             for migration_id in reversed_migration_ids:
                 migration_module = migration_modules[migration_id]
                 response = await migration_module.forwards()
@@ -131,10 +133,10 @@ async def run_backwards(
                 "apps:\n"
                 f"{', '.join(names)}\n"
                 "Are you sure you want to continue? [y/N] "
-            )
+            ).lower()
         )
 
-        if _continue not in "yY":
+        if _continue != "y":
             return MigrationResult(success=False, message="user cancelled")
         for _app_name in sorted_app_names:
             print_heading(_app_name)