committer-date-is-author-date flag removes email in "Commit"

committer-date-is-author-date flag removes email in "Commit"

What did you do before the bug happened? (Steps to reproduce your issue)
* Create empty repo using `git init`
* Make few commits, at least two
* execute `git log --format=fuller`
* Notice the log, with "Author", "AuthorDate", "Commit", "CommitDate"
* Note, "Commit"
* execute `git rebase --committer-date-is-author-date HEAD~1`
* execute `git log --format=fuller`
* Note, email from "Commit" is empty <>

What did you expect to happen? (Expected behavior)
* Email must not be removed.

What happened instead? (Actual behavior)
* email got removed/replaced with empty `< >`

What's different between what you expected and what actually happened?

Expected:
```
Author:     VenomVendor <info@VenomVendor.com>
AuthorDate: Thu Oct 22 19:41:05 2020 -0200
Commit:     VenomVendor <info@VenomVendor.com>
CommitDate: Thu Oct 22 19:41:05 2020 -0200
```

Happened (Missing email in Commit)
```
Author:     VenomVendor <info@VenomVendor.com>
AuthorDate: Thu Oct 22 19:41:05 2020 -0200
Commit:     VenomVendor <>
CommitDate: Thu Oct 22 19:41:05 2020 -0200
```

Anything else you want to add:

``` $ cd ~

$ mkdir committer-date-is-author-date-bug

$ cd committer-date-is-author-date-bug

$ git --version git version 2.29.0

$ git init Initialized empty Git repository in ~/committer-date-is-author-date-bug/.git/

$ git log --format=fuller fatal: your current branch 'master' does not have any commits yet

$ TEXT=1; echo "${TEXT}" > sample.txt && git add . && git commit -m 
"${TEXT}"
[master (root-commit) 20731cb] 1
  1 file changed, 1 insertion(+)
  create mode 100644 sample.txt

$ TEXT=2; echo "${TEXT}" > sample.txt && git add . && git commit -m 
"${TEXT}"
[master e3d8ce8] 2
  1 file changed, 1 insertion(+), 1 deletion(-)

$ TEXT=3; echo "${TEXT}" > sample.txt && git add . && git commit -m 
"${TEXT}"
[master 30f2b84] 3
  1 file changed, 1 insertion(+), 1 deletion(-)

$ git log --format=fuller
commit 30f2b84e360d2ea79fe3355b5fbfa5cdb401c65f (HEAD -> master)
Author:     VenomVendor <info@VenomVendor.com>
AuthorDate: Thu Oct 22 19:41:05 2020 -0200
Commit:     VenomVendor <info@VenomVendor.com>
CommitDate: Thu Oct 22 19:41:05 2020 -0200

     3

commit e3d8ce88ea25b14cf2840ccd41cebc8f68663b8e
Author:     VenomVendor <info@VenomVendor.com>
AuthorDate: Thu Oct 22 19:41:02 2020 -0200
Commit:     VenomVendor <info@VenomVendor.com>
CommitDate: Thu Oct 22 19:41:02 2020 -0200

     2

commit 20731cb051e42dd5435dec4157aa58203e5fc60d
Author:     VenomVendor <info@VenomVendor.com>
AuthorDate: Thu Oct 22 19:40:59 2020 -0200
Commit:     VenomVendor <info@VenomVendor.com>
CommitDate: Thu Oct 22 19:40:59 2020 -0200

     1

$ git rebase --committer-date-is-author-date HEAD~2 Current branch master is up to date, rebase forced. Successfully rebased and updated refs/heads/master.

$ git log --format=fuller
commit be24ee5cd9b76b0f11599b4f8af2609f6c5f3b06 (HEAD -> master)
Author:     VenomVendor <info@VenomVendor.com>
AuthorDate: Thu Oct 22 19:41:05 2020 -0200
Commit:     VenomVendor <>
CommitDate: Thu Oct 22 19:41:05 2020 -0200

     3

commit c45d01b6969281d11fc78f60cb0c4d830f216892
Author:     VenomVendor <info@VenomVendor.com>
AuthorDate: Thu Oct 22 19:41:02 2020 -0200
Commit:     VenomVendor <>
CommitDate: Thu Oct 22 19:41:02 2020 -0200

     2

commit 20731cb051e42dd5435dec4157aa58203e5fc60d
Author:     VenomVendor <info@VenomVendor.com>
AuthorDate: Thu Oct 22 19:40:59 2020 -0200
Commit:     VenomVendor <info@VenomVendor.com>
CommitDate: Thu Oct 22 19:40:59 2020 -0200

     1
```

Please review the rest of the bug report below. You can delete any lines you don't wish to share.

[System Info] git version: git version 2.29.0 cpu: x86_64 no commit associated with this build sizeof-long: 8 sizeof-size_t: 8 shell-path: /bin/sh uname: Darwin 19.6.0 Darwin Kernel Version 19.6.0: Mon Aug 31 22:12:52 PDT 2020; root:xnu-6153.141.2~1/RELEASE_X86_64 x86_64 compiler info: clang: 12.0.0 (clang-1200.0.32.2) libc info: no libc information available $SHELL (typically, interactive shell): /bin/zsh

[Enabled Hooks]

-VenomVendor