Check existence of the index of array.

[metheglin]

Hello.
The below code sample throws the Exception because there is much bigger value(3424) in array than specified max value(2000).

require 'histogram/array'
values = [
  1113,
  789,
  319,
  3424,
  1166,
  1610,
  719,
]
values.histogram( 8, min: 0, max: 2000 )
  # NoMethodError: undefined method `+' for nil:NilClass

Simply, this problem could be avoided by checking the existence of index.
How do you think?