Why is pushing to stash not allowed without an initial commit?

[Abhijeet Sonar <abhijeet.nkt@gmail.com>]

I recently ran `git stash push` in a newly initialized repository.

```
$ git init
Initialized empty Git repository in <redacted>/.git/
$ touch a b
$ git add a
$ git stash push a
You do not have the initial commit yet
```


On the other hand, with an initial commit:

```
$ git init
Initialized empty Git repository in <redacted>/.git/
$ touch a b
$ git add a
$ git commit -m a
[master (root-commit) 3bf80c1] a
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 a
$ git add b
$ git stash
Saved working directory and index state WIP on master: 3bf80c1 a
$ git log --oneline --graph --all
*   293076b (refs/stash) WIP on master: 3bf80c1 a
|\  
| * 64140e0 index on master: 3bf80c1 a
|/  
* 3bf80c1 (HEAD -> master) a
```

I see that the stash commit has two parents: the initial commit and the
commit that actually holds the files that were stashed.

If git were to allow a stash entry with no initial commit, it would have to
create a stash commit with only one parent (i.e. the commit labeled with
'index on <branch>'). I wonder if there is a reason this would be bad and
therefore not allowed?

Thanks.