Applying User Picker to Report Sections

Hi All, 

I'm trying to add a User Picker filter that applies to 4 different sections of a report, all of which are backed by different DSE's or Views. It was suggested to me to use the a!pickerFieldUsers field to do this, so in my Dashboard I added this filter:

            a!columnLayout(
              contents: {
                a!pickerFieldUsers(
                  label: "Study Monitor",
                  instructions: "Type any study monitor name",
                  labelPosition: "ABOVE",
                  value: local!studymonitor,
                  saveInto: local!studymonitor
                )
              }
            ),

Then for the first Bar Chart I'm trying to apply the filter to, I added the Rule Input of "selectedStudyMonitors" and wanted to compare this value that's fed in from the Filter selections to the "studyMonitor" field of the view that's backing this Chart like this: 

if(
                isNull(
                  ri!selectedStudyMonitors
                ),
                {},
                a!queryFilter(
                  field: "studyMonitor",
                  operator: "includes",
                  value: ri!selectedStudyMonitors
                  
                )
              )

But I'm getting this error below; I originally tried "=" but it didn't like that operator either. I checked that the data values being returned in both interfaces are the User Names, so something like "first.last" or "monitor.one" etc -- they should match/be able to be compared using either = or includes, right? 

Thanks for any help!