panic in object.getFileStatsFromFilePatches() for commits updating submodules: both from and to are nil

[krylovsk]

Got this error on some private repository with submodules for commits that only update submodules refs: both from and to files are nil here https://github.com/src-d/go-git/blob/master/plumbing/object/patch.go#L278

Here is the panic stacktrace:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x30 pc=0x110fe8e]

goroutine 1 [running]:
gopkg.in/src-d/go-git.v4/plumbing/object.getFileStatsFromFilePatches(0xc4203b8a00, 0x1, 0x1, 0xc42032b830, 0x0, 0x0)
	/Users/krylovsk/src/gopkg.in/src-d/go-git.v4/plumbing/object/patch.go:278 +0x43e
gopkg.in/src-d/go-git.v4/plumbing/object.(*Patch).Stats(0xc42032b830, 0x0, 0x1, 0xc42032b830)
	/Users/krylovsk/src/gopkg.in/src-d/go-git.v4/plumbing/object/patch.go:111 +0x41
main.main()
	/tmp/git-test/main.go:38 +0x35a
exit status 2

[krylovsk]

UPD: looks like the issue appears in commits that update submodules refs

[ferhatelmas]

@mcuadros @ajnavarro What is the idea to fix ?

Handling this case in commit stats by skipping since non-file changes are returning no meaningful information (#317) ?

[krylovsk]

Looks like the issue also affects binary files, created a PR that ignores patches with zero chunks. Makes sense?