猫鼬-如何告诉猫鼬跳过空参数(如果有)

询问

Location.find(
   {
      "$text":{
         "$search":"req.body.searchKey"
      },
      "location_type":"req.body.location_type",
      "address.state_ut":"req.body.state_ut",
      "address.city":"req.body.city"
   }
)

I am taking these filters (location_type, city, state_ut) from user. User may only want to filter result with location_type then state_ut and city will remains null and I want mongoose to skip these parameters which are null. Which is the proper way to do this. I don't want to write many queries by checking with if statements.