Python code: TypeError: unsupported operand type(s) for *: 'NoneType' and 'float'

hi, I am new to Python at beginner level and following Mr Mosh tutorials.
while I am following Mr Mosh coding a simple project that involves automation that process thousands of spreadsheets in under a second, and do act in accordance with him step by step. Although the codes mine and his are the same but when I run the code I am getting something like:

corrected_price = cell.value * 0.9
TypeError: unsupported operand type(s) for *: ‘NoneType’ and ‘float’

can anyone help me with this part please