Summery field set to NULL

Hi,

How do i provide a summary with the JSON results? I want to display this on the search results page (e.g. under the title, a summary of matching text found within the result page content) I’ve added -SM=meta to the query processor options:

-stem=2 -SM=meta -SF=[department,departmentkey,email,imgurl,name,…]

But summary is still set to NULL in the JSON:

{
...
          "results": [
                {
                    "rank": 1,
                    "score": 1000,
                    "title": ...
                    "summary": null,

Is there any query processor option that I’ve missed out?