have an actual `NullColumn` object and update docs accordingly.

Follow up to #15438 and #15502.

/cc @sgrif

1 files changed, 6 insertions, 0 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/column.rb b/activerecord/lib/active_record/connection_adapters/column.rb
index 3b0dcbc6a7..5e4e00bc64 100644
--- a/activerecord/lib/active_record/connection_adapters/column.rb
+++ b/activerecord/lib/active_record/connection_adapters/column.rb
@@ -55,6 +55,12 @@ module ActiveRecord
         type_cast(default)
       end
     end
+
+    class NullColumn < Column
+      def initialize(name)
+        super name, nil, Type::Value.new
+      end
+    end
   end
   # :startdoc:
 end