Added a test that shows how two selects with different keys throw a KeyNotFoundException
Return an empty enumerable instead of throwing a KeyNotFoundException when grouping requests with different keys

Fixes #183
Rename the test to something more meaningful
Fixed the method name casing
Removed accidentally added usings
Merge pull request #184 from flagbug/getcreatedat-keynotfoundexception-test

Ensure that GetCreatedAt never throws