Oracle Solution for Error ora-31670

ORA-31670: Username argument must be specified and non-null.

What triggered the Error:

Called change user with a NULL username or a null string.

What should we do to fix it:

Specify a valid username argument. If this error occurs from a Data Pump client (e.g. expdp or impdp), try the operation again. If the error occurs again, contact Oracle Customer Support and report the error.