Constraint NOT NULL missing

Data Pump Import With EXCLUDE=CONSTRAINT Or INCLUDE=CONSTRAINT Is Excluding And Respectively Not Including NOT NULL Constraints (Doc ID 1930631.1)

After doing a Data Pump import (impdp) in 12.1.0.2 database release with parameter EXCLUDE=CONSTRAINT the NOT NULL constraints from source tables are not in target tables. Sequence of steps leading to the problem:
– Data Pump export of tables with NOT NULL and referential integrity constraints
– Data Pump import with EXCLUDE=CONSTRAINT

http://blog.umairmansoob.com/data-dump-import-missing-not-null-constraints/