optional args in lambdas.rb

# this works
a = lambda{ |b| b*3 }
# => #<Proc:0x01f5f540@(irb):125>
a.call 4
# => 12

# strangely, this does too (with a warning)
a.call 4, 6
# (irb):125: warning: multiple values for a block parameter (2 for 1)
#        from (irb):131
# => [4, 6, 4, 6, 4, 6]

# but this doesn't -- you need at least the one argument.
a.call
# (irb):133: warning: multiple values for a block parameter (0 for 1)
#        from (irb):134
# NoMethodError: You have a nil object when you didn't expect it!
# You might have expected an instance of Array.
# The error occurred while evaluating nil.*
#        from (irb):133
#        from (irb):134:in `call'
#        from (irb):134
#        from :0

# compare:
a = lambda{ |*b| (b.first||23)*3 }
# => #<Proc:0x01f3fa38@(irb):135>
a.call 4
# => 12
a.call       # can call with no args now
# => 69