add a helpful error for register()
add a helpful error for register()

hustxiaoc/tchannel,RyanTech/tchannel,bunnyblue/tchannel,chenwenbin928/tchannel,i/tchannel,vanloswang/tchannel,chenwenbin928/tchannel,RyanTech/tchannel,chenwenbin928/tchannel,savaki/tchannel,sasa233/tchannel,i/tchannel,i/tchannel,sasa233/tchannel,benfleis/tchannel,bunnyblue/tchannel,vanloswang/tchannel,benfleis/tchannel,Zirpon/tchannel,savaki/tchannel,Zirpon/tchannel,vanloswang/tchannel,sasa233/tchannel,RyanTech/tchannel,hustxiaoc/tchannel,bunnyblue/tchannel,hustxiaoc/tchannel,savaki/tchannel,Zirpon/tchannel,benfleis/tchannel