我刚刚安装了Ruby on Rails v5，但是当我运行Rails服务器并转到浏览器时，会出现此错误吗？
def retrieve_connection(spec_name) #:nodoc:
pool = retrieve_connection_pool(spec_name)
raise ConnectionNotEstablished, "No connection pool with id #{spec_name} found." unless pool
conn = pool.connection
raise ConnectionNotEstablished, "No connection for #{spec_name} in connection pool" unless conn
conn