Change the below to use ErrorCodes::StreamProcessorInvalidOptions, which is a user error:

    if (fieldPaths)

{         uassert(8186209,                 "Cannot find index to verify that join fields will be unique",                 fieldsHaveSupportingUniqueIndex(expCtx, outputNs, *fieldPaths));         return
{*fieldPaths, boost::none}

;
    }