Check not null in column

I’m working on android and I have to retrieve a row where a column is not null. I have attached a screenshot of my backendless console. Thanks in advance.

‘solvedBy’ is relational object linked to the user. I have searched and finds out ‘is not’ for ‘!=’. It works for String but it is not working for relations.

!= works for relations using the following format in whereClase:

relatedColumnName.objectId is not null

Regards,
Mark