block_problem.rb

def foo(option, &block)
  if block_given? bar(option, &block)
  else
    bar(option)
  end
end
def bar(option, &block)
  p option
  block.call if block_given?
end

> foo(3)
3
# ArgumentError: wrong number of arguments(1 for 0)
#from (pry):25:in `block_given?'

> foo(3) { puts "tick" }
3
tick
#ArgumentError: wrong number of arguments(1 for 0)
#from (pry):25:in `block_given?'

def taz(option, &block)
  p option
  block.call if block_given?
end

taz(3) { puts "FOO" }
3
FOO
#=> nil