[CONNECT C++] ECQuery::CreateQuery()

I want to "query" for ANY EC data on an existing element that belongs to a specific schema. I see where one can find ALL ECClass'es on an element by:

ECQuery::CreateQuery(ECQUERY_PROCESS_SearchAllClasses);

and one can search for a SPECIFIC SchemaName and class by:

ECQuery::CreateQuery( SchemaName, ClassName );

But is it possible to search for ANY/ALL classes of a Schema that *may* be on an element?

ECQuery::CreateQuery( SchemaName, nullptr );

that variation does not find any ECClasses of SchemaName on an element.

Thanks,