The argument type ‘Set?’ can’t be assigned to the parameter type ‘Set’

Solution for The argument type ‘Set?’ can’t be assigned to the parameter type ‘Set
is Given Below:

When i try to assign set of markers to markers argument in GoogleMap it gives me this error…enter image description here
The argument type ‘Set?’ can’t be assigned to the parameter type ‘Set’.

Code Sample

body: GoogleMap(
    initialCameraPosition: CameraPosition(
      target: LatLng(
        widget.initialLocation!.latitude!,
        widget.initialLocation!.longitude!,
      ),
      zoom: 16,
    ),
    onTap: widget.isSelecting! ? _selectLocation : null,
    
    markers: _pickedLocation == null
        ? null
        : {
            Marker(
              markerId: MarkerId('m1'),
              position: _pickedLocation!,
            ),
          },
  ),

markers: (_pickedLocation == null && !widget.isSelecting)
        ? <Marker>[].toSet()
        : [
            Marker(
              markerId: MarkerId('m1'),
              position: _pickedLocation ??
                  LatLng(
                    widget.initialLocation.latitude!,
                    widget.initialLocation.longitude!,
                  ),
            ),
          ].toSet(),