I want to use default popup info functionality to query WMS layer with getFeatureInfo request.
The request sent after clicking the map contains "INFO_FORMAT=undefined".
Unfortunately the service doesn't accept this value. And this is only parameter which prevents service from response.
The prefered value for this parameter is "text/plain".
I've tried using customLayerParameter (new in 3.18) when defining the service, but it doesn't overwrite default "undefined" value.
So my question is: how to define INFO_FORMAT parameter equal "text/plain" for getFeatureInfo request?