Schema nullability is ignored in BigQuery Sink plugin

We observed a couple of issues with single root-cause:

Case 1:
BigQuery table does not exist, BigQuery Sink always creates table with nullable fields, though some fields from source might have been required.
Source schema: a int not null
BigQuery schema: a int

Case 2:
BigQuery table exists and has at least one column which is required. Does not matter which nullability such column has in source, pipeline fails.
Source schema: a int not null
BigQuery schema: a int not null

Some basic STR:

• Create BigQuery Table (see schema sample)

• Create pipeline that use this schema (see attached sample)

• Execute and found that BiqQuery sink plugin ignore nullable checkbox in configured schema (see attached log)