Most of cases we should propagate null when call `NewInstance`, and so far there is only one case we should stop null propagation: create product/java bean. So I think it makes more sense to propagate null by dafault.

This also fixes a bug when encode null array/map, which is firstly discovered in https://github.com/apache/spark/pull/10401

Author: Wenchen Fan <wenchen@databricks.com>

Closes #10443 from cloud-fan/encoder.