Add assertion.
Add assertion.

RyanCavanaugh/TypeScript,microsoft/TypeScript,kpreisser/TypeScript,kitsonk/TypeScript,Microsoft/TypeScript,RyanCavanaugh/TypeScript,kitsonk/TypeScript,RyanCavanaugh/TypeScript,SaschaNaz/TypeScript,weswigham/TypeScript,kpreisser/TypeScript,microsoft/TypeScript,weswigham/TypeScript,kitsonk/TypeScript,Microsoft/TypeScript,Microsoft/TypeScript,SaschaNaz/TypeScript,kpreisser/TypeScript,weswigham/TypeScript,SaschaNaz/TypeScript,SaschaNaz/TypeScript,microsoft/TypeScript