Issue title: Application crash is you change the theme
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##### **Overview of the issue**
The application Crashed when we try to add theme by editing src/main/webapp/index.html. The HTML throws the following error "An error has occured :-("
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##### **Motivation for or Use Case**

We need to update the current theme while preserving the features like type-scripting.  However we can not even add a simple text in the HTML page. SOS

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##### **Reproduce the error**

Just open "src/main/webapp/index.html", add a simple html/text in the file. Re-run the application and get an exception/error.

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  [JSFiddle](http://jsfiddle.net/)? -->

##### **Related issues**

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##### **Suggest a Fix**

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  causing the problem (line of code or commit) -->

##### **JHipster Version(s)**

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##### **JHipster configuration, a `.yo-rc.json` file generated in the root folder**

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##### **Entity configuration(s) `entityName.json` files generated in the `.jhipster` directory**

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##### **Browsers and Operating System**

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 Comments: 
 Comment 0: Can you describe what you are trying to do and how to reproduce your issue exactly?
 Comment 1: Provide browser's console log and also all details that have been requested by the issue template.
 Comment 2: C'mon, there isn't even the version number... We just can't work like that.
 Comment 3: This ticket has been closed as the guidelines are not followed.

Tickets must follow our [Guidelines](https://github.com/jhipster/generator-jhipster/blob/master/CONTRIBUTING.md#submitting-an-issue), as mentioned in:

1. our [Readme file on the front page of the project](https://github.com/jhipster/generator-jhipster/blob/master/README.md), 
2. the ["create a new ticket" page](https://github.com/jhipster/generator-jhipster/issues/new) and
3. our [Help page](http://jhipster.github.io/help/)

We have also created a template on the ["create a new ticket" page](https://github.com/jhipster/generator-jhipster/issues/new) to help you follow those guidelines.
{'source': 'GithubIssues', 'repo_name_with_owner': 'jhipster/generator-jhipster', 'issue_id': 191659517, 'repo_stars': 20060.0}