cloudtools/troposphere — pull request #116 by tobias-jimdo (2014-08-18 12:17:12+00:00)
Title: makes MasterUsername and MasterPassword optional

, since they are not required if you create an RDS instance from a snapshot

http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-rds-database-instance.html#cfn-rds-dbinstance-masterusername