public void updateNull(String columnName) throws SQLException {
        throw new UnsupportedOperationException();
    }
Sets the designated nullable column in the current row or the
insert row of this <code>CachedRowSetImpl</code> object with
<code>null</code> value.
<P>
This method updates a column value in the current row or the insert
row of this rowset, but it does not update the database.
If the cursor is on a row in the rowset, the
method {@link #updateRow} must be called to update the database.
If the cursor is on the insert row, the method {@link #insertRow}
must be called, which will insert the new row into both this rowset
and the database.

@param columnName a <code>String</code> object that must match the
       SQL name of a column in this rowset, ignoring case
@throws SQLException if (1) the given column name does not match the
           name of a column in this rowset, (2) the cursor is not on
           one of this rowset's rows or its insert row, or (3) this
           rowset is <code>ResultSet.CONCUR_READ_ONLY</code>
src/main/java/org/replicadb/rowset/sun/rowset/internal/SyncResolverImpl.java