def optional_belongs_to(*symbols, &block)
        options = symbols.extract_options!
        options.merge!(optional: true)
        belongs_to(*symbols, options, &block)
      end
def optional_belongs_to(*symbols, &block)
        options = symbols.extract_options!
        options.merge!(optional: true)
        belongs_to(*symbols, options, &block)
      end
A quick method to declare optional belongs to.