class Sinatra::CommonLogger

if another CommonLogger is already in the middleware chain.
Behaves exactly like Rack::CommonLogger with the notable exception that it does nothing,

def call(env) 

def call(env)
  env['sinatra.commonlogger'] ? @app.call(env) : super
end

def call(env) 

def call(env)
  env['sinatra.commonlogger'] = true
  call_without_check(env)
end