Patch for the pg truncation adapter to prevent an emtpy list of table…

…s from

generating an illegal TRUCATE TABLE statement.

lib/database_cleaner/active_record/truncation.rb

@@ -96,6 +96,7 @@ def truncate_table(table_name)
       end
 
       def truncate_tables(table_names)
+        return if table_names.nil? || table_names.empty?
         execute("TRUNCATE TABLE #{table_names.map{|name| quote_table_name(name)}.join(', ')} #{restart_identity} #{cascade};")
       end