Can not install grub-efi-amd64-signed package to /target

[jundong.wu]

While installing GRUB in UEFI mode, the tip dialog came to me. And there is a EFI partition already,I don't what I did wrong. I met this bug at 18.04, and I reported it, but you didn't fix it. Now could you fix this as soon as possible, because it really caused a big trouble!

ProblemType: Bug
DistroRelease: Ubuntu 18.10
Package: ubiquity 18.10.12
ProcVersionSignature: Ubuntu 4.18.0-10.11-generic 4.18.12
Uname: Linux 4.18.0-10-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.10-0ubuntu13
Architecture: amd64
CasperVersion: 1.399
Date: Sun Oct 21 02:28:30 2018
InstallCmdLine: BOOT_IMAGE=/casper/vmlinuz file=/cdrom/preseed/ubuntu.seed boot=casper quiet splash ---
LiveMediaBuild: Ubuntu 18.10 "Cosmic Cuttlefish" - Release amd64 (20181017.3)
SourcePackage: grub-installer
UpgradeStatus: No upgrade log present (probably fresh install)