method.rb

class A; end

class B
  def hoge
    # do something
  end
end

class C
  def hoge(*vals)
    # do something
  end
end

class D
  attr_accessor :v
  def fuga(val=nil)
    v.try(:xx) || v.hoge(*val)
  end
end

b = B.new
c = C.new
d = D.new
d.v = b
d.fuga(1)
d.v = c
d.fuga

method2.rb

2.2.2 [1] pry(main)> def hoge; :hoge; end
=> :hoge
2.2.2 [2] pry(main)> v = nil
=> nil
2.2.2 [3] pry(main)> hoge(*v)
=> :hoge
2.2.2 [4] pry(main)> (*v)
SyntaxError: unexpected '\n', expecting '='
2.2.2 [4] pry(main)> [*v]
=> []

2.2.2 [5] pry(main)> def hoge(a)
2.2.2 [5] pry(main)*   p a
2.2.2 [5] pry(main)* end
=> :hoge
2.2.2 [6] pry(main)> hoge(*nil)
ArgumentError: wrong number of arguments (0 for 1)
from (pry):5:in `hoge'

2.2.2 [7] pry(main)> def hoge(*a)
2.2.2 [7] pry(main)*   p a
2.2.2 [7] pry(main)* end
=> :hoge
2.2.2 [8] pry(main)> hoge(*nil)
[]
=> []

A継承させるの忘れた