Add feature for implied null (needed for Firebird backend)

2 files changed, 5 insertions, 2 deletions

diff --git a/django/db/backends/__init__.py b/django/db/backends/__init__.py
index dfc967e60a..1b12a41caf 100644
--- a/django/db/backends/__init__.py
+++ b/django/db/backends/__init__.py
@@ -646,6 +646,9 @@ class BaseDatabaseFeatures(object):
     # Suffix for backends that don't support "SELECT xxx;" queries.
     bare_select_suffix = ''
 
+    # If NULL is implied on columns without needing to be explicitly specified
+    implied_column_null = False
+
     uppercases_column_names = True
 
     def __init__(self, connection):
diff --git a/django/db/backends/schema.py b/django/db/backends/schema.py
index 2a62803a73..dcf3ad544b 100644
--- a/django/db/backends/schema.py
+++ b/django/db/backends/schema.py
@@ -132,9 +132,9 @@ class BaseDatabaseSchemaEditor(object):
         if (field.empty_strings_allowed and not field.primary_key and
                 self.connection.features.interprets_empty_strings_as_nulls):
             null = True
-        if null:
+        if null and not self.connection.features.implied_column_null:
             sql += " NULL"
-        else:
+        elif not null:
             sql += " NOT NULL"
         # Primary key/unique outputs
         if field.primary_key: