[BUG] TypeError: expected string or bytes-like object when entering e.g. "ä, ü, ö"

[Mangosniper]

I have issues when entering some characters e.g. into in Input. These characters are not only german umlaute like "ä, ü, ö" but also shift, arrow-up and some more. The error is:

Input two letters: Traceback (most recent call last):
  File "test.py", line 9, in <module>
    prompt()
  File "test.py", line 6, in prompt
    var_two_letters = two_letters.launch()
  File "/home/administrator/.local/lib/python3.6/site-packages/bullet/client.py", line 444, in launch
    if self.valid(result):
  File "/home/administrator/.local/lib/python3.6/site-packages/bullet/client.py", line 417, in valid
    if not bool(re.match(self.pattern, ans)):
  File "/usr/lib/python3.6/re.py", line 172, in match
    return _compile(pattern, flags).match(string)
TypeError: expected string or bytes-like object

Minimal code to reproduce ist:

from bullet import Input

two_letters = Input(prompt = "Input two letters: ", pattern="^[A-Z]{2}$")

def prompt():
    var_two_letters = two_letters.launch()
    print(var_two_letters)

prompt()

Actually, I dont even want to enter such characters, as you can see that the regex in the pattern only accepts plain characters. However, the script crashes when I just type in the character, so there is no way for me to sanitize the input before the crash.

Is there anything I can do about this? I tried the native "input" function of pything and here I can add Umlaute.