check empty lists for hlist constraints
check empty lists for hlist constraints

clhodapp/shapeless,Atry/shapeless,alexarchambault/shapeless,lambdista/shapeless,triggerNZ/shapeless,wheaties/shapeless,malcolmgreaves/shapeless,notxcain/shapeless,roberth/shapeless,khronnuz/shapeless,joescii/shapeless,isaka/shapeless,milessabin/shapeless,tek/shapeless,liff/shapeless,TomasMikula/shapeless,lukasz-golebiewski/shapeless,fthomas/shapeless