Issue while adding custom HTTP headers for call REST service - Studio pro 10 (beta) on mac

Hello,

I'm new to Mendix and I'm using Studio pro 10.11.0 (Beta) on Mac.

I have an issue with adding a new custom HTTP headers: 'application/json'

The IDE keeps throwing the following error: Expression error(s).

Screenshot: As you may notice the red comma at the beginning of the line looks like a backtick. This is because the text editor keeps changing the apostrophe while typing.

Thanks in advance for any explanations and suggestions.