Save blank value in dropdown using Patch function

AgeGroup: {
            '@odata.type': "#Microsoft.Azure.Connectors.SharePoint.SPListExpandedReference",
               Id: -1,
               Value: ""
          },
Multiple Filter
Sort(
    Filter(
        EmployeeDetails,
        txtLenelSegmentSearch.Text in LenelSegment,
        txtSearchSiteCode.Text in SiteCode,
        txtSearchLenelSegment.Text in LenelSegment,
        txtSearchSwitchType.Text in SwitchType,
        txtSearchMake.Text in Make,
        txtSearchModel.Text in Model,
        txtSearchDefaultGateway.Text in DefaultGateway,
        txtSearchIPAddress.Text in IPAddress
    ),
    ID,
    Descending
)
Append custom value in the dropdown
Ungroup(
     Table(
         {DropdownOptions: [""]},
         {DropdownOptions: Choices(CapitalExpenditureRequests.'Type of Request')}
     ),
     "DropdownOptions"
 )
Saving the value in choice column
 'Type of Request': {
                    Value: ddTypeOfRequest.Selected.Value,
                    '@odata.type': "#Microsoft.Azure.Connectors.SharePoint.SPListExpandedReference"
                },