No variables causes null reference when serving a recipe

[JasonPagel]

Creating a recipe without variables causes "Cannot convert undefined or null to object" when serving the recipe.

(node:1948) UnhandledPromiseRejectionWarning: TypeError: Cannot convert undefined or null to object
at Function.keys ()
at BakePackage.objToVariableMap (C:\temp\test\node_modules\azure-bake\dist\bake-loader.js:72:30)
at BakePackage._loadPackage (C:\temp\test\node_modules\azure-bake\dist\bake-loader.js:118:25)
at new BakePackage (C:\temp\test\node_modules\azure-bake\dist\bake-loader.js:20:14)
at C:\temp\test\node_modules\azure-bake\dist\index.js:198:19
at Generator.next ()
at C:\temp\test\node_modules\azure-bake\dist\index.js:8:71
at new Promise ()
at __awaiter (C:\temp\test\node_modules\azure-bake\dist\index.js:4:12)
at run (C:\temp\test\node_modules\azure-bake\dist\index.js:187:12)
(node:1948) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 2)
(node:1948) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.