Why can't I converter theIEnumable to a list ?

        public IEnumerable GetErrors(string propertyName)
        {
            return _propertyErrors.GetValueOrDefault(propertyName, null);
        }

GetErrors(nameof(Name)).ToList();

        public IEnumerable GetErrors(string propertyName)
        {
            return _propertyErrors.GetValueOrDefault(propertyName, null);
        }

GetErrors(nameof(Name)).ToList();