[Help-bash] Why empty key is not allowed?

[Peng Yu]

Hi,

I am trying to assign an empty key to an associated array.

$ declare -A x
$ x[]=1
-bash: x[]: bad array subscript

But I got this error. Is it not allowed? Or I am not doing it correctly?

The manpage says this. So empty string should be allowed?

"associative arrays are referenced using arbitrary strings."

Thanks.

-- 
Regards,
Peng