opencv-python: TypeError: can only join an iterable

#==================Errors====================

Exception in Tkinter callback

Traceback (most recent call last):
  File "C:\Users\Joy\AppData\Local\Programs\Python\Python39\lib\tkinter\__init__.py", line 1892, in __call__
    return self.func(*args)
  File "c:\Users\Joy\Desktop\Student Attendance System\Student Attendance System\face_recognition.py", line 119, in face_recog
    img=recognize(img,clf,faceCascade)
  File "c:\Users\Joy\Desktop\Student Attendance System\Student Attendance System\face_recognition.py", line 108, in recognize
    coord=draw_boundray(img,faceCascade,1.1,10,(255,25,255),"Face",clf)
  File "c:\Users\Joy\Desktop\Student Attendance System\Student Attendance System\face_recognition.py", line 79, in draw_boundray
    n="+".join(n)
TypeError: can only join an iterable
[ WARN:0] global C:\New folder\opencv-master\modules\videoio\src\cap_msmf.cpp (438) `anonymous-namespace'::SourceReaderCB::~SourceReaderCB terminating async callback

#===================================code============================

def face_recog(self):
        def draw_boundray(img,classifier,scaleFactor,minNeighbors,color,text,clf):
            gray_image=cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
            features=classifier.detectMultiScale(gray_image,scaleFactor,minNeighbors)
            
            coord=[]

            for (x,y,w,h) in features:
                cv2.rectangle(img,(x,y),(x+w,y+h),(0,255,0),3)
                id,predict=clf.predict(gray_image[y:y+h,x:x+w])
                confidence=int((100*(1-predict/300)))

                conn=mysql.connector.connect(host="localhost",username="root",password="**********",database="face_recognizer")
                my_cursor=conn.cursor()


                my_cursor.execute("select Name from student where Student_Id="+str(id))
                n=my_cursor.fetchone()
                n="+".join(n)

                my_cursor.execute("select Roll from student where Student_Id="+str(id))
                r=my_cursor.fetchone()
                r="+".join(r)

                my_cursor.execute("select Department from student where Student_Id="+str(id))
                d=my_cursor.fetchone()
                d="+".join(d)

                my_cursor.execute("select Student_Id from student where Student_Id="+str(id))
                i=my_cursor.fetchone()
                i="+".join(i)

                if confidence>77:
                    cv2.putText(img, f"ID:{i}",(x,y-75),cv2.FONT_HERSHEY_COMPLEX,0.8,(255,255,255),3)
                    cv2.putText(img, f"Roll:{r}",(x,y-55),cv2.FONT_HERSHEY_COMPLEX,0.8,(255,255,255),3)
                    cv2.putText(img, f"Name:{n}",(x,y-30),cv2.FONT_HERSHEY_COMPLEX,0.8,(255,255,255),3)
                    cv2.putText(img, f"Department:{d}",(x,y-5),cv2.FONT_HERSHEY_COMPLEX,0.8,(255,255,255),3)
                    self.mark_attendance(i,r,n,d)
                else:
                    cv2.rectangle(img,(x,y),(x+w,y+h),(0,0,255),3)
                    cv2.putText(img,"Unknown Face",(x,y-55),cv2.FONT_HERSHEY_COMPLEX,0.8,(255,255,255),3)
                
                coord=[x,y,w,h]

            return coord
        
        def recognize(img,clf,faceCascade):
            coord=draw_boundray(img,faceCascade,1.1,10,(255,25,255),"Face",clf)
            return img

        faceCascade=cv2.CascadeClassifier("haarcascade_frontalface_default.xml")
        clf=cv2.face.LBPHFaceRecognizer_create()
        clf.read("classifier.xml")

        video_cap=cv2.VideoCapture(0)

        while True:
            ret,img=video_cap.read()
            img=recognize(img,clf,faceCascade)
            cv2.imshow("Welcome To Face Recognition",img)
            
            if cv2.waitKey(1) & 0xFF == ord('q'):
                break
            
            
        video_cap.release()
        cv2.destroyAllWindows()