After upgrading Jenkins to version 2.332.4.1

it turned out that one can't refer to variable representing a form file parameter type using 'params.file_param'.

For example given parameters:

properties([
    parameters([
        string(name: 'string_param', description: ''),
        file(name: 'file_param', description: '')
    ])
])

When we try to access it via params:

params.string_param // it works and returns param value
params.file_param // is always null

results with null value no matter whether file is attached or not.

Why it is not working? Is there another way of accessing form parameters?