EclipseLink used to print count like this a while ago, but always uses a field in the count now.
What database are you using? You could log a bug for support for a count(*) on the database platform.
You could override the count yourself, but it will be a little tricky. You will need to define an ExpressionOperator and add it to the ExpressionOperator operators to override the Count operator. You could just print COUNT(*) in your operator. You will also need to override the printCollection method in your own Count ExpressionOperator subclass.