Controller `render()` is setting the Content-Type to `text/html` by default even with non-html content

[ColinHarrington]

Task List

• Steps to reproduce provided
• Example that reproduces the problem uploaded to Github
• Full description of the issue provided (see below)

Steps to Reproduce

1. Use the render() method specifying a view but without a contentType
2. Utilize a gson view or non-html view
3. Observe that the Content-Type is set to text/html
4. Without specifying the view name (relying on the convention) the Content-Type is set appropriately

Expected Behaviour

The Content-Type should be set by the view layer

Actual Behaviour

The Content-Type is defaulted to 'text/html'

Environment Information

• Operating System: Linux
• Grails Version: 3.1+
• JDK Version: 1.8

Example Application

• https://github.com/ColinHarrington/grails-core-issue-10337

Exposed in grails-views after 1.1.2
apache/grails-views#93

[ColinHarrington]

You can also see the difference of behavior between using the conventions to chose the view vs using the render() method in this test in grails3-functional-tests