gistfile1.txt

$ git init .
Initialized empty Git repository in /home/kawakami/temp/test/.git/

$ touch init

$ git add init

$ git commit -m 'initial commit'
[master (root-commit) 4c0c59e] initial commit
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 init

$ git commit -m 'empty commit' --allow-empty
[master a9a6943] empty commit

$ touch somefile

$ git add somefile

$ git commit -m 'nonempty on top'
[master f2fe53a] nonempty on top
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 somefile

$ git lg
* f2fe53a - (HEAD -> master) nonempty on top (1 second ago) <Cesar Kawakami>
* a9a6943 - empty commit (14 seconds ago) <Cesar Kawakami>
* 4c0c59e - initial commit (24 seconds ago) <Cesar Kawakami>

$ git show HEAD^
commit a9a694399502707e53e8cdd213c81b2e04f8d1c2
Author: Cesar Kawakami <kawakami@fb.com>
Date:   Thu Oct 26 11:44:03 2017 -0700

    empty commit

$ git rebase -i 4c0c59e
Stopped at a9a6943... empty commit
You can amend the commit now, with

        git commit --amend

Once you are satisfied with your changes, run

        git rebase --continue


$ git commit --amend
interactive rebase in progress; onto 4c0c59e
Last command done (1 command done):
   e a9a6943 empty commit
Next command to do (1 remaining command):
   pick f2fe53a nonempty on top
You are currently editing a commit while rebasing branch 'master' on '4c0c59e'.

No changes
You asked to amend the most recent commit, but doing so would make
it empty. You can repeat your command with --allow-empty, or you can
remove the commit entirely with "git reset HEAD^".

$ git commit --amend --allow-empty
[detached HEAD 8776c75] empty commit edited
 Date: Thu Oct 26 11:44:03 2017 -0700

$ git rebase --continue
Successfully rebased and updated refs/heads/master.

$ git lg
* d469064 - (HEAD -> master) nonempty on top (2 seconds ago) <Cesar Kawakami>
* 8776c75 - empty commit edited (9 seconds ago) <Cesar Kawakami>
* 4c0c59e - initial commit (87 seconds ago) <Cesar Kawakami>