Don't provide an error callback if not provided in options.
Don't provide an error callback if not provided in options.

paulovieira/tilemill-clima,mbrukman/tilemill,tilemill-project/tilemill,paulovieira/tilemill-clima,fxtentacle/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,nyimbi/tilemill,Zhao-Qi/tilemill,MappingKat/tilemill,florianf/tileoven,Teino1978-Corp/Teino1978-Corp-tilemill,mbrukman/tilemill,tizzybec/tilemill,MappingKat/tilemill,tizzybec/tilemill,nyimbi/tilemill,MappingKat/tilemill,paulovieira/tilemill-clima,florianf/tileoven,nyimbi/tilemill,mbrukman/tilemill,paulovieira/tilemill-clima,tilemill-project/tilemill,tizzybec/tilemill,fxtentacle/tilemill,MappingKat/tilemill,Zhao-Qi/tilemill,nyimbi/tilemill,fxtentacle/tilemill,Zhao-Qi/tilemill,paulovieira/tilemill-clima,tilemill-project/tilemill,fxtentacle/tilemill,nyimbi/tilemill,Zhao-Qi/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,tizzybec/tilemill,mbrukman/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,florianf/tileoven,Teino1978-Corp/Teino1978-Corp-tilemill,mbrukman/tilemill,fxtentacle/tilemill,MappingKat/tilemill,Zhao-Qi/tilemill,tizzybec/tilemill