Minor Description
Currently ConfigurationBuilder does not seem to have any support optional configuration.
TangImpl.NewConfigurationBuilder(params IConfiguration[]) eventually calls ConfiguraitonBuilder constructor which expects all configs to be non-null (throws Null Reference Exception otherwise)
In IMRU scenario code generating configs (JobDefinitionBuilder) and code assembling config (ReefClient) is separated and the client code is forced to double check if configuration in job definition was provided (if that configuration is optional) .
It would be nice to provide allow optional configurations either implicitly (by ignoring null configs) or explicitly by adding specific API (AddOptionalConfiguration) which would ignore nulls.
if we want to keep things as is force client to do the checks, we should probably fix the constructor to throw ArgumentException instead of NullReference exception.