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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _fix_unecessary_blank_lines(ps: PromptSession) -> None: """This is a fix for additional empty lines added by prompt toolkit. This assumes the layout of the default session doesn't change, if it does, this needs an update."""


    default_container = ps.layout.container

    default_buffer_window = \
        default_container.get_children()[0].content.get_children()[1].content

    assert isinstance(default_buffer_window, Window)
    # this forces the main window to stay as small as possible, avoiding
    # empty lines in selections
    default_buffer_window.dont_extend_height = Always()