MultiIndex [] method working with invalid indexes

[lokeshh]

[1] pry(main)> d =        Daru::MultiIndex.from_tuples([
[1] pry(main)*     [:c,:one,:bar],            
[1] pry(main)*     [:c,:one,:baz],            
[1] pry(main)*     [:c,:two,:foo],            
[1] pry(main)*     [:c,:two,:bar]            
[1] pry(main)* ])     
=> Daru::MultiIndex:18229240 (levels: [[:c], [:one, :two], [:bar, :baz, :foo]]
labels: [[0, 0, 0, 0], [0, 0, 1, 1], [0, 1, 2, 0]])
[2] pry(main)> v = Daru::Vector.new([1,2,3,4], index: d)
=> 
#<Daru::Vector:18002080 @name = nil @size = 4 >
                              nil
[:c, :one, :bar]                1
[:c, :one, :baz]                2
[:c, :two, :foo]                3
[:c, :two, :bar]                4

[4] pry(main)> v[:x, :one]
=> 
#<Daru::Vector:17572840 @name = nil @size = 2 >
          nil
[:bar]      1
[:baz]      2

But :x is not a valid index.