How to fix Matplotlib Error caused by the button release event when embeded in tkinter

Hello I'm making a GUI with tkinter and with matplotlib embeded. I have a FigureCanvas that I use to graph various things depending on the users inputs. Everything seems to work fine excepts for a weird error that doesn't seems to have much of an impact. Here is the code:

import tkinter as tk
import tkinter.ttk as ttk
from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg
from matplotlib.figure import Figure
import numpy as np


class App:
    def __init__(self, root):
        self.root = root
        #
        self.combo = ttk.Combobox(root, values=["2D 1", "2D 2", "3D"], state = "readonly")
        self.combo.bind("<<ComboboxSelected>>", self.change_graph)
        self.combo.pack()
        #
        self.fig = Figure()
        self.ax = self.fig.add_subplot()
        self.drawing_area = FigureCanvasTkAgg(self.fig, master=root)
        self.drawing_area.get_tk_widget().pack()
        #
        self.axis_3D = False

    def change_graph(self, event):
        graph_selected = self.combo.get()
        if graph_selected == "2D 1":
            if self.axis_3D:
                self.ax.remove()
                self.ax = self.fig.add_subplot()
                self.axis_3D = False
            else:
                self.ax.clear()
            x = np.linspace(0, 10, 100)
            y = 4 + 2 * np.sin(2 * x)
            self.ax.plot(x, y, c="r")
            self.ax.axis("equal")
            self.drawing_area.draw()
        elif graph_selected == "2D 2":
            if self.axis_3D:
                self.ax.remove()
                self.ax = self.fig.add_subplot()
                self.axis_3D = False
            else:
                self.ax.clear()
            x = np.linspace(0, 10, 500)
            y = -4 + 2 * np.sin(2 * x)
            self.ax.plot(x, y, c="b")
            self.ax.axis("auto")
            self.drawing_area.draw()
        else:
            if self.axis_3D:
                self.ax.clear()
            else:
                self.ax.remove()
                self.ax = self.fig.add_subplot(projection="3d")
                self.axis_3D = True
            x = np.linspace(0, 10, 500)
            y = 4 + 2 * np.sin(2 * x)
            z = 2*x
            self.ax.plot(x, y, z, c="b")
            self.drawing_area.draw()


root = tk.Tk()
root.geometry("800x600")
app = App(root)
root.mainloop()

The problem I'm having is that after the 3D graph is selected and then a 2D graph is selected back, every time the graph is panned it gives an error which I don't understand. The error is the following:

Traceback (most recent call last):
  File "...\matplotlib\cbook\__init__.py", line 287, in process
    func(*args, **kwargs)
  File "...\mpl_toolkits\mplot3d\axes3d.py", line 1165, in _button_release
    toolbar = getattr(self.figure.canvas, "toolbar")
AttributeError: 'NoneType' object has no attribute 'canvas'