Erreur tkinter

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Users\Erwan\Anaconda3\lib\tkinter\__init__.py", [/download/telecharger-34098305-line line] 1705, in __call__
    return self.func(*args)
  File "C:/Users/Erwan/Documents/_developement/_python/-tkinter/tkinter_10.py", line 5, in addition
    label_var.set(entry_var.get() +  entry1_var.get())
  File "C:\Users\Erwan\Anaconda3\lib\tkinter\__init__.py", line 529, in get
    return self._tk.getdouble(self._tk.globalgetvar(self._name))
_tkinter.TclError: expected floating-point number but got ""

import tkinter

#----------------------def____--------------------------------------
def addition(*argms):
    label_var.set(entry_var.get() +  entry1_var.get())

def plus_n():
    a = label_var.get()
    b = entry1_var.get()
    c = (a + b)
    print (c)
    label_var.set(c)

def multiplication(*argms):
    label_multi_var.set(multip_var.get() * multip1_var.get())

def fois_n():
    d = label_multi_var.get()
    e = multip1_var.get()
    f = (d * e)
    print (f)
    label_multi_var.set(f)



#----------------------root.tkinter-----------------------------------
root = tkinter.Tk()
root.geometry("600x200")
root.minsize(200, 150)
root.maxsize(1280, 720)
root.title("Projet calcul")

#-----------------------addition--------------------------------------
label_add = tkinter.Label(root, text="    Addition    ")

entry_var = tkinter.DoubleVar()
entry_var.trace("w", addition)
entry = tkinter.Entry(root, textvariable=entry_var)

entry1_var = tkinter.DoubleVar()
entry1_var.trace("w", addition)
entry1 = tkinter.Entry(root, textvariable=entry1_var)

signe = tkinter.Label(root, text="+")

button = tkinter.Button(root, text="+x", background="blue", foreground="white",activebackground="white",activeforeground="black",
command = plus_n)


mainframe = tkinter.LabelFrame(root, height=50)

label_var = tkinter.DoubleVar()
label_result = tkinter.Label(mainframe, textvariable=label_var)



label_add.grid(row=0, column=0)
entry.grid(row=0, column=1)
signe.grid(row=0, column=2)
entry1.grid(row=0, column=3)
mainframe.grid(row=0, column=4)
label_result.grid()
button.grid(row=0, column=5)


#----------------------------multiplication---------------------------------
label_multi = tkinter.Label(root, text="    Multiplication    ")

multip_var = tkinter.DoubleVar()
multip_var.trace("w", multiplication)
multi = tkinter.Entry(root, textvariable=multip_var)

signe = tkinter.Label(root, text="x")

multip1_var = tkinter.DoubleVar()
multip1_var.trace("w", multiplication)
multi1 = tkinter.Entry(root, textvariable=multip1_var)

mainframe_multi = tkinter.LabelFrame(root, height=50)

label_multi_var = tkinter.DoubleVar()
label_multi_result = tkinter.Label(mainframe_multi, textvariable=label_multi_var)

button1 = tkinter.Button(root, text="*x", background="blue", foreground="white",activebackground="white",activeforeground="black",
command = fois_n)



label_multi.grid(row=1, column=0)
multi.grid(row=1, column=1)
signe.grid(row=1, column=2)
multi1.grid(row=1, column=3)
mainframe_multi.grid(row=1, column=4)
label_multi_result.grid()
button1.grid(row=1, column=5)

#-----------------------end------------------------------------------------
button_quit = tkinter.Button(root, text="Quit", command=root.destroy, background="red", foreground="white", activebackground="white",activeforeground="black")
button_quit.grid(sticky="s")
root.mainloop()