    # File lib/active_record/connection_adapters/sqlite_adapter.rb, line 272
          def change_column_null(table_name, column_name, null, default = nil)
            unless null || default.nil?
              execute("UPDATE #{quote_table_name(table_name)} SET #{quote_column_name(column_name)}=#{quote(default)} WHERE #{quote_column_name(column_name)} IS NULL")
            end
            alter_table(table_name) do |definition|
              definition[column_name].null = null
            end
          end