[1.7.x] Fixed #23738 -- Allowed migrating from NULL to NOT NULL with the same default value

Thanks to Andrey Antukh for the report.

Backport of 715ccfde24 from master

1 files changed, 1 insertions, 1 deletions

diff --git a/django/db/backends/schema.py b/django/db/backends/schema.py
index 154f452967..64ba5b0740 100644
--- a/django/db/backends/schema.py
+++ b/django/db/backends/schema.py
@@ -613,7 +613,7 @@ class BaseDatabaseSchemaEditor(object):
                 # directly run a (NOT) NULL alteration
                 actions = actions + null_actions
             # Combine actions together if we can (e.g. postgres)
-            if self.connection.features.supports_combined_alters:
+            if self.connection.features.supports_combined_alters and actions:
                 sql, params = tuple(zip(*actions))
                 actions = [(", ".join(sql), reduce(operator.add, params))]
             # Apply those actions