Python object not recognized as JPG despite previous manipulations

I am writing a program that pastes one jpeg onto another, however one of my functions stops recognizing an object as a jpeg file for unknown reasons.

My output is

"inside_select_letter_to_paste, letter to paste is a <class ‘NoneType’>.

and then

AttributeError: ‘NoneType’ object has no attribute ‘save’

Why is letter_to_paste not being recognized as a JPEG object despite the lines to open it and resize it as a thumbail working properly?

Thanks.

def select_letter_to_paste():

    letter_to_paste = Image.open(f'{letter_folder}\TEST-A.jpg')
    letter_to_paste = letter_to_paste.thumbnail((100,100))
    print(f'inside select_letter_to_paste, letter_to_paste is a {type(letter_to_paste)}.')
    letter_to_paste.save('test_letter.jpg')

  return letter_to_paste

>Solution :

Image.thumbnail modifies the image in-place and returns None.

The line

letter_to_paste = letter_to_paste.thumbnail((100,100))

is assigning None to letter_to_paste. Change it to

letter_to_paste.thumbnail((100,100))