validate_route_conditions

# File actionpack/lib/action_controller/routing/builder.rb, line 182
        def validate_route_conditions(conditions)
          if method = conditions[:method]
            [method].flatten.each do |m|
              if m == :head
                raise ArgumentError, "HTTP method HEAD is invalid in route conditions. Rails processes HEAD requests the same as GETs, returning just the response headers"
              end

              unless HTTP_METHODS.include?(m.to_sym)
                raise ArgumentError, "Invalid HTTP method specified in route conditions: #{conditions.inspect}"
              end
            end
          end
        end