Note: for support questions, please use one of these channels: https://github.com/angular/angular.js/blob/master/CONTRIBUTING.md#question. This repository's issues are reserved for feature requests and bug reports.

Do you want to request a feature or report a bug?

What is the current behavior?
empty template are treated as not exist in templateCache

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem via https://plnkr.co or similar (template: http://plnkr.co/edit/tpl:yBpEi4).
create a empty template, use template cache. and it is treated as not cached

What is the expected behavior?
should be treated as cached

What is the motivation / use case for changing the behavior?
i think this is a bug.

Which versions of Angular, and which browser / OS are affected by this issue? Did this work in previous versions of Angular? Please also test with the latest stable and snapshot (https://code.angularjs.org/snapshot/) versions.
multiple version include the latest

Other information (e.g. stacktraces, related issues, suggestions how to fix)
in $TemplateRequestProvider

this condition
if (!isString(tpl) || !$templateCache.get(tpl))

should be if (!isString(tpl) || !isUndefiend($templateCache.get(tpl)))