[IoTDB-1518] Session null pointer when create timeseries

In org.apache.iotdb.session.Session, createMultiTimeseries don't support encoding or compressor to be null, which will throw null pointer error. But in client, it is supported to create series without encoding and compressor. The details are as follows



Start at org.apache.iotdb.session.Session and inspect createMultiTimeseries, focusing on how null encoding and compressor values are handled. Reproduce the reported null-pointer case and verify that creating timeseries without those values succeeds without changing supported client behavior.

Written by the indexing model from the issue text.