Update account.rb

if number is nil, you will set @bank_number to 0 (same for @bank_account_number)

2.0.0p247 :001 > number = nil
 => nil 
2.0.0p247 :002 > nr_str = "#{number}".gsub(/\s/,'')
 => "" 
2.0.0p247 :003 > @bank_number = nr_str.to_i
 => 0 
2.0.0p247 :004 >