presto-google-sheets/src/main/java/io/prestosql/plugin/google/sheets/SheetsRecordCursor.java/SheetsRecordCursor/isNull
class SheetsRecordCursor:    @Override
    public boolean isNull(int field)
    {
        checkArgument(field < columnHandles.size(), "Invalid field index");
        return Strings.isNullOrEmpty(getFieldValue(field));
    }