Expression<Set<SimpleEnum>> simpleEnums = root.get( Person_.enumCollection);

// Using the correct collection of enums and an enum parameter
cq.where(cb.isMember(SimpleEnum.A, simpleEnums));
// leads to SQLSyntaxErrorException: incompatible data type in conversion in hsqldb

Expression<Set<SimpleEnum>> simpleEnums = root.get( Person_.enumCollection);

// Using the correct collection of enums and an enum parameter
cq.where(cb.isMember(SimpleEnum.A, simpleEnums));
// leads to SQLSyntaxErrorException: incompatible data type in conversion in hsqldb

// Here tricking hibernate, telling that it is a collection of strings and passsing a string argument.
Expression<Collection<String>> simpleEnums = root.get("enumCollection");

cq.where(cb.isMember("A", simpleEnums));
// no exception and correct return valus