Whitespace changes
Extracted get_layout method
No need to interpolate a string
get_session_data and set_session_data methods should be together
Simplified setter
FROM: session[key] = @display == nil ? session[key] : @display
TO: session[key] = @display unless @display.nil?
Convert if x is not nil to unless x.nil?
Create variable for readability
Changed to use Ruby's OR pattern
FROM: x == nil ? default : x
TO: x || default