Error using dictionary in an IQueryable.Select () method to design chosen columns at runtime

The code fragment below is intended to use the Select () method to perform generic column projections on a query, according to a list of given column names. The program works fine if all the columns are of type 'string', but triggers the exception below when some column is of a different type, like 'Guid'.

  

Expression of type 'System.Guid' can not be used for parameter of type   'System.Object' of method 'Void Add (System.String, System.Object)

How can I solve this problem?

public static IQueryable EscolherColunas<T>(this IQueryable<T> baseQuery, String[] columns) where T : class 
{
    var parameter = Expression.Parameter(typeof(T), "t");
    var addMethod = typeof(Dictionary<string, object>).GetMethod("Add");
    List<ElementInit> dicadds = new List<ElementInit>();
    foreach (var column in columns)
    {
        var eKey = Expression.Constant(column);
        var eValue = Expression.Property(parameter, column);
        var eAdd = Expression.ElementInit(addMethod, eKey, eValue);
        dicadds.Add(eAdd);
    }
    var dicinit = Expression.ListInit(Expression.New(typeof(Dictionary<string, object>)), dicadds);
    var selector = Expression.Lambda<Func<T, dynamic>>(dicinit, parameter);
    return baseQuery.Select(selector);
}