FilteredElementCollector returns ElementType instead of Elements

Hi, i'm trying to make a function that returns a list of elements that have the omniclass BuiltInParameter not set to something empty, i made this function but it's returning a list of the ElementTypes not the Elements themselves.

If anyone could help that would be great.

public List<Element> GetElementsWithThisParameter(Document doc, BuiltInParameter param)
{
     ParameterValueProvider provider = new ParameterValueProvider(new ElementId((int)param));

     FilterStringRule rule1 = new FilterStringRule(provider, new FilterStringEquals(), "", true);
     ElementParameterFilter filter1 = new ElementParameterFilter(rule1, true);

     return
        (new FilteredElementCollector(doc))
        .WherePasses(filter1)
        .ToElements() as List<Element>;
}