Use existing #empty_insert_statement_value for an insert with no columns.

[metaskills]

Aaron, following up from our email exchange.
Arel has logic that does not include columns for an insert statement if they are empty. 

  def visit_Arel_Nodes_InsertStatement o
    [ "INSERT INTO #{visit o.relation}",
      ( "(#{o.columns.map { |x|
      quote_column_name x.name
    }.join ', '})" unless o.columns.empty?),
      (visit o.values if o.values),
    ].compact.join ' '
  end

The SQL Server adapter defines the older #empty_insert_statement_value method as such. This is because there is no such thing as "VALUES(DEFAULT)" that would work.

  def empty_insert_statement_value
    "DEFAULT VALUES"
  end

In the latest version of rails we are no longer using this but #null_insert_value instead and AR is hooking into it from ActiveRecord::Relation#insert like so.

  if values.empty? # empty insert
    im.values = im.create_values [connection.null_insert_value], []
  else
    im.insert substitutes
  end

This gives no one a chance to construct something like #empty_insert_statement_value for the SQLServerAdapter. We should utilize the existing #empty_insert_statement_value instead which seems more inline with Arel's InsertManager too.

[tenderlove]

should be merged, so closing.