set query params to some combogrid without overriding existing value

[Opan Mustopah]

hello again,
i have a problem with queryparams properties.

firstly here is my code:

Code:

$('#on_behalf_id').combogrid({
      onSelect:function(index,row){
        //if (state.op == 'show_form'){return false;}
        console.log('behalf');
        $('#on_behalf_address_id').combogrid({
          url:'#{lookup_address_path}',
          queryParams:{
            bp_id: row.bp_id,
            type:'movement'
          }
        }).combogrid('enable');
      }
    });

    $('#on_behalf_address_id').combogrid({
      onSelect:function(index,row){
        if (state.op == 'show_form'){return false;}

        if (row.phone == '-' && row.fax == '-' && row.address_line_1 == '-'){
          $('#on_behalf_address_det').textbox('setValue','-');            
        }else{
          $('#on_behalf_address_det').textbox('setValue',row.address_line_1+' '+row.address_line_2+','+row.city_name+','+row.province_name+', '+row.zip+', '+row.country_name+' PHONE: '+row.phone+', FAX: '+row.fax);            
        }
      }
    });

just said on_behalf_address_id is already a value, but when on_behalf_id send a new queryParams to on_behalf_address_id, the existing value on on_behalf_address_id is empty, can i do it without make existing value dissappear?

many thanks for the answer.