A Method with an Optional Parameter

Besides the more obvious option of parameters with default values, that Sawa has already shown, using arrays or hashes might be handy in some cases. Both solutions preserve nil as a an argument.

1. Receive as array:

def some_func(*args)
  puts args.count
end

some_func("x", nil)
# 2

2. Send and receive as hash:

def some_func(**args)
  puts args.count
end

some_func(a: "x", b: nil)
# 2

You can also use a hash as argument and have more freedom:

def print_arg(args = {})
  if args.has_key?(:age)
    puts args[:age]
  end
end

print_arg 
# => 
print_arg(age: 35, weight: 90)
# => 35