Error using first example in Readme

[AriCohen8]

Hello, thank you for the package.

I get an error using your first example:
RatingBar(
initialRating: 3,
direction: Axis.horizontal,
allowHalfRating: true,
itemCount: 5,
itemPadding: EdgeInsets.symmetric(horizontal: 4.0),
itemBuilder: (context, _) => Icon(
Icons.star,
color: Colors.amber,
),
onRatingUpdate: (rating) {
print(rating);
},
);

Error points to row 119 of the package claiming withAlpha is being called on null. When I put in the unratedcolor parameter it works. Not sure if this is to do with my usage or a bug in the plugin?

[sarbagyastha]

Duplicate of #13 .