Thread 1:EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0) what went wrong?

Question

I got this sigabrt error : Thread 1:EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0) as shown in the view did load

The code is responsible for following an unfollowing users The sigabrt error occurs during segue from the search View to the user profile view where i can follow or unfollow that user

var loggedinuser : FIRUser?
var otheruser :  NSDictionary?
var  loggedinuserdata : NSDictionary?
var databaseref : FIRDatabaseReference!
@IBOutlet weak var name: UILabel!
@IBOutlet weak var followorunfollow: UIButton!


override func viewDidLoad() {
    super.viewDidLoad()

    self.databaseref = FIRDatabase.database().reference()

    databaseref?.child("users").child(self.loggedinuser!.uid).observe(.value, with: { (snapshot) in :Thread 1:EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0) 

        self.loggedinuserdata?.setValue(self.loggedinuser!.uid, forKey: "uid" )
    }) { (error) in
        print(error.localizedDescription)
    }



    databaseref?.child("users").child(self.otheruser?["uid"] as! String).observe(.value, with: { (snapshot) in

        let uid =  self.otheruser?["uid"] as! String
        self.otheruser = snapshot.value as? NSDictionary
        self.otheruser?.setValue(uid, forKey: "uid")

    }) { (error) in
        print(error.localizedDescription)
    }

    databaseref?.child("following").child(self.loggedinuser!.uid).child(self.otheruser?["uid"] as! String).observe(.value, with: { (snapshot) in

        if(snapshot.exists())
        {
            self.followorunfollow.setTitle("follow", for : UIControlState())
        }
        else
        {
            self.followorunfollow.setTitle("unfollow", for : UIControlState())

        }



    }) { (error) in
        print(error.localizedDescription)
    }


    self.name.text = self.otheruser?["name"] as? String


}

@IBAction func didtapfollow(_ sender: Any) {
    let followerref = "followers/\(self.otheruser?["uid"] as! String)/\(self.loggedinuserdata?["uid"] as! String)"
    let followingref =  "following/" + (self.loggedinuserdata?["uid"] as! String) + "/" + (self.otheruser?["uid"] as! String )

    if(self.followorunfollow.titleLabel?.text == "follow")
    {

        let followerdata = ["name" : self.loggedinuserdata?["name"] as! String, "pc " :" \(self.loggedinuserdata?["pc"])"]

        let followingdata = ["name" : self.otheruser?["name"] as! String, "pc ":" \(self.otheruser?["pc"])"]


        let childupdates = [followerref: followerdata,
                            followingref:followingdata]


        databaseref?.updateChildValues(childupdates)

        let followerscount:Int?
        let followingcount:Int?

        if(self.otheruser?["followerscount"]  == nil )
        {
            followerscount = 1
        }
        else {
            followerscount =  self.otheruser?["followerscount"] as! Int + 1
        }
        if(self.loggedinuserdata?["followingcount"] == nil)
        {
            followingcount = 1
        }

        else {
            followingcount =  self.loggedinuserdata?["followingcount"] as! Int -  1
        }

        databaseref?.child("users").child(self.loggedinuserdata?["uid"]  as! String).child("followingcount").setValue(followingcount)
        databaseref?.child("users").child(self.otheruser?["uid"]  as! String).child("followerscount").setValue(followerscount)

    }


    else
    {

        databaseref?.child("users").child(self.loggedinuserdata?["uid"]  as! String).child("followingcount").setValue(self.loggedinuserdata!["followingcount"] as! Int - 1)

        databaseref?.child("users").child(self.otheruser?["uid"]  as! String).child("followerscount").setValue(self.otheruser!["followerscount"] as! Int - 1 )



        _ = "followers/\(self.otheruser?["uid"] as! String)/\(self.loggedinuserdata?["uid"] as! String )"

        let followingref =  "following/" + (self.loggedinuserdata?["uid"] as! String) + "/" + (self.otheruser?["uid"] as! String )



        let childupdates = [followingref: NSNull(),
                            followerref:NSNull()]


        databaseref?.updateChildValues(childupdates)
    }


}

}