Invalid column type with Spring Repository and native query with WHERE IN

Question

I'm trying to write a native query in Spring @Repository that uses a WHERE IN condition, but I can't figure out what syntax must be used. I tried the following:

@Query(nativeQuery=true, value="select ext_id,count(*) from table where ext_id in (?1) group by ext_id")
List<Object[]> get(Collection<Long> extIdList);

And

List<Object[]> get(Collection<BigDecimal> extIdList);

But I keep having the error "Invalid column type".

If I switch to named parameters with where ext_id in (:ids) and

List<Object[]> get(@Param("ids") Collection<Long> extIdList);

I get the error "SQL Error: Missing IN or OUT parameter"

What's the proper way to have the above query executed?