Problem with SQLSetPos on block cursor with NULL values

If one of fields continue NULL and not NULL values that can cause different issues on positional operations on block cursor when positions changes between rows with NULL and not NULL values.
If such field is part of unique index SQL_DELETE operation with 0 row number(all rows) will not act correctly - it can either skip all rows and return error or even crash(depending on what rows go first).
If position set using SQL_POSITION operation, SQLGetData may return wrong result on such field.