Fixed Copy::listContents return type on non existing dir.
Fixed Copy::listContents return type on non existing dir.

barryvdh/flysystem,mhlavac/flysystem,twistor/flysystem,nao-pon/flysystem,Amrit01/flysystem,sachintaware/flysystem,mhlavac/flysystem,mapyo/flysystem,sohelrana820/flysystem,hannesvdvreken/flysystem,dshafik/flysystem,twistor/flysystem,CarsonF/flysystem,oswaldderiemaecker/flysystem,dstockto/flysystem,rossriley/flysystem,farmisen/flysystem