# File lib/thinking_sphinx/adapters/postgresql_adapter.rb, line 38
    def convert_nulls(clause, default = '')
      default = case default
      when String
        "'#{default}'"
      when NilClass
        'NULL'
      when Fixnum
        "#{default}::bigint"
      else
        default
      end
      
      "COALESCE(#{clause}, #{default})"
    end