How to resolve Git reporting invalid sha1 pointer 0000000000000000000000000000000000000000?

Question

My computer shut down suddenly and now the Git repository of the project which I worked on is defect. I have Git 2.20.1 installed. I immediately created a backup copy of the project folder to play around with the original. I have local branches which I do not want to loose.

$ git status
error: object file .git/objects/c7/8e67bcad2ea132e3df8f80bb42b4804ab4f2a3 is empty
fatal: loose object c78e67bcad2ea132e3df8f80bb42b4804ab4f2a3 (stored in .git/objects/c7/8e67bcad2ea132e3df8f80bb42b4804ab4f2a3) is corrupt

Shorted output:

$ git fsck --name-objects
error: object file .git/objects/04/f338bf0dc0770b841b291af6cdd4c9130edb84 is empty
error: unable to mmap .git/objects/04/f338bf0dc0770b841b291af6cdd4c9130edb84: No such file or directory
error: 04f338bf0dc0770b841b291af6cdd4c9130edb84: object corrupt or missing: .git/objects/04/f338bf0dc0770b841b291af6cdd4c9130edb84
error: object file .git/objects/2e/07479ec010e5b459387d841a576e1ead97f850 is empty
error: unable to mmap .git/objects/2e/07479ec010e5b459387d841a576e1ead97f850: No such file or directory
error: 2e07479ec010e5b459387d841a576e1ead97f850: object corrupt or missing: .git/objects/2e/07479ec010e5b459387d841a576e1ead97f850
error: object file .git/objects/34/b03409d09382c44f50409e4388850ca9c82c77 is empty
error: unable to mmap .git/objects/34/b03409d09382c44f50409e4388850ca9c82c77: No such file or directory
...
error: object file .git/objects/c7/8e67bcad2ea132e3df8f80bb42b4804ab4f2a3 is empty
error: unable to mmap .git/objects/c7/8e67bcad2ea132e3df8f80bb42b4804ab4f2a3: No such file or directory
error: c78e67bcad2ea132e3df8f80bb42b4804ab4f2a3: object corrupt or missing: .git/objects/c7/8e67bcad2ea132e3df8f80bb42b4804ab4f2a3
error: object file .git/objects/e5/19b2fbf083f68694af97ccddf46bc28c6ee8f7 is empty
error: unable to mmap .git/objects/e5/19b2fbf083f68694af97ccddf46bc28c6ee8f7: No such file or directory
error: e519b2fbf083f68694af97ccddf46bc28c6ee8f7: object corrupt or missing: .git/objects/e5/19b2fbf083f68694af97ccddf46bc28c6ee8f7
error: object file .git/objects/ec/289b8e8d17c47644d5bdbfbfc8b2957d2a430e is empty
error: unable to mmap .git/objects/ec/289b8e8d17c47644d5bdbfbfc8b2957d2a430e: No such file or directory
error: ec289b8e8d17c47644d5bdbfbfc8b2957d2a430e: object corrupt or missing: .git/objects/ec/289b8e8d17c47644d5bdbfbfc8b2957d2a430e
error: object file .git/objects/ed/33778ddc07a26a37c6f200f35ffee12e365ea4 is empty
error: unable to mmap .git/objects/ed/33778ddc07a26a37c6f200f35ffee12e365ea4: No such file or directory
error: ed33778ddc07a26a37c6f200f35ffee12e365ea4: object corrupt or missing: .git/objects/ed/33778ddc07a26a37c6f200f35ffee12e365ea4
error: object file .git/objects/f6/5686bed85025fd7adbf209ba93846b18800d70 is empty
error: unable to mmap .git/objects/f6/5686bed85025fd7adbf209ba93846b18800d70: No such file or directory
error: f65686bed85025fd7adbf209ba93846b18800d70: object corrupt or missing: .git/objects/f6/5686bed85025fd7adbf209ba93846b18800d70
error: object file .git/objects/fd/cdc518b01c670cd38c15903fd3e84554114d38 is empty
error: unable to mmap .git/objects/fd/cdc518b01c670cd38c15903fd3e84554114d38: No such file or directory
error: fdcdc518b01c670cd38c15903fd3e84554114d38: object corrupt or missing: .git/objects/fd/cdc518b01c670cd38c15903fd3e84554114d38

Checking object directories: 100% (256/256), done.
Checking objects: 100% (40855/40855), done.
error: refs/remotes/origin/colors-housekeeping: invalid sha1 pointer 0000000000000000000000000000000000000000
error: bad ref for .git/logs/refs/remotes/origin/colors-housekeeping
error: object file .git/objects/ec/289b8e8d17c47644d5bdbfbfc8b2957d2a430e is empty
fatal: loose object ec289b8e8d17c47644d5bdbfbfc8b2957d2a430e (stored in .git/objects/ec/289b8e8d17c47644d5bdbfbfc8b2957d2a430e) is corrupt

colors-housekeeping is a branch which is already merged to master and already I edited other files afterwards, committed and merged another branch.

What are the steps I can take to fix the corrupt objects?

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Answer 1

This occurred for me when a repo I had cloned renamed its default branch from master to main.

The error was:

error: refs/remotes/origin/HEAD: invalid sha1 pointer 0000000000000000000000000000000000000000

Let's look at that pointer file on disk:

$ cat .git/refs/remotes/origin/HEAD
ref: refs/remotes/origin/master

After editing that file and replacing master with main, I was once again able to fetch/fsck/gc without errors.

Answer 2

error: unable to mmap... is one error, invalid sha1 pointer 000000... is another.

For anyone (like me) who is here who has only the sha1-pointer-error but no mmap-errors:

The sha1-pointer-error might mean that the expected pointer-file does not exist. refs/remotes/origin/colors-housekeeping probably contains content like:
ref: refs/remotes/origin/notexistingbranch
or:
6ca0197d8f15f381d67e3502e678ca3d17dbbea2
but this file (ref) or commit-id can not be found. In both cases you can fix the error by writing any known commit-id or pointer to a valid commit-id in the file. In other words, you reassign the cached value of the commit of the branch origin/colors-housekeeping. When you fetch from origin git will write the correct commit-id of origin/colors-housekeeping in refs/remotes/origin/colors-housekeeping again.