Null is converted to empty string when writing to database.

An easy workaround to query entities with empty ( null ) text fields is to use the following query filter:

a!queryFilter(
    field: "name",
    operator: "in",
    value: {"", null}
)

How to do similar thing for Integer? If an integer field is empty or null, I don't want it return in query

One fun thing you can do is run it through filternulls() after you have it out of the query.  It shouldn't be THAT much overhead to return a list of nulls from your query, but "IS NULL" and "IS NOT NULL" should be fine if you are querying an integer row. 

Perhaps wrapping the query in toInteger() would also help.  That should at least theoretically convert null type Text into null type Integer.

One fun thing you can do is run it through filternulls() after you have it out of the query.  It shouldn't be THAT much overhead to return a list of nulls from your query, but "IS NULL" and "IS NOT NULL" should be fine if you are querying an integer row. 

Perhaps wrapping the query in toInteger() would also help.  That should at least theoretically convert null type Text into null type Integer.