[ 2374940 ] Empty key names accepted

JSON:

`"" : "value"`

Result:

`DotDict({'': 'value'})`

Empty strings are accepted as key name. Here I have doubts.

Cross check:

`"   " : "value"`

Result:

`Error: 'Invalid key name: "   ". Key names have to start with a letter, digit or underscore.'!`

That is OK, and in my opinion also an empty string should be an invalid key name.
