presto-main/src/main/java/io/prestosql/type/UnknownType.java/UnknownType/equalTo
class UnknownType:    @Override
    public boolean equalTo(Block leftBlock, int leftPosition, Block rightBlock, int rightPosition)
    {
        // Check that the position is valid
        checkArgument(leftBlock.isNull(leftPosition), "Expected NULL value for UnknownType");
        checkArgument(rightBlock.isNull(rightPosition), "Expected NULL value for UnknownType");
        return true;
    }