for the example you provided given that the methods invoked by the <routes> are classmethod I commonly do something along the lines of 

    <Route Url="/error/list" Method="GET" Call="GetErrors" />

ClassMethod GetErrors(pStartTime As %UTC = "", pEndTime As %UTC = "") As %Status

{

    #DIM tSC                    As %Status = $$$OK

    #DIM eException             As %Exception.AbstractException

    #DIM %request               As %CSP.Request

    Try {

            Set:$Get(%response)'="" %response.ContentType="application/json"

            If $Get(%request) {

                Set tStartDate = $Get(%request.Data("StartTime",1))

                Set tStopDate = $Get(%request.Data("EndTime",1))

            }

            Else {

                #;If they are defined in the parameter list

                If pStartTime'="" Set tStartDate=pStartTime

                If pEndTime'="" Set tStopDate=pEndTime

            }

removeEmpty is defined as 

The <table> removeEmpty attribute controls whether or not the empty nodes that Zen encounters in the XML data for this report display in the XHTML or PDF output generated by this <table> in the report. If removeEmpty is:

• Not specified, the <table> inherits the removeEmpty value of its parent. If no element in the ancestry of this <table> specifies a removeEmpty value, then the default value, 0, applies to this <table>.
• 0, empty element and attribute values are output to the XHTML or PDF generated for this <table> in the report.
• 1, empty element and attribute values are not output to the XHTML or PDF generated for this <table> in the report. If orient is "row," any rows with all empty data values are omitted from the output. If orient is "col," any columns with all empty data values are omitted from the output. If there are some empty cells, but the entire row (or column) is not empty, then the row (or column) is displayed with the empty cells blank.

The group attribute must be set for removeEmpty to work.

This attribute has the underlying data type %ZEN.Datatype.booleanOpens in a new tab. See “Zen Reports Attribute Data Types.”

so I dont think removeEmpty addresses what you have asked.  I would consider using an 

ifxpath expression that would control whether or not to display the table