add a default value to all params

[emilos]

We're breaking the pure rule in many cases, e.g. in the simple method:

function first (array) {
  return array[0]
}

the following code would throw when there's no array, or something else was passed.

Acceptance criteria

• add default values to functions in array.js, collection.js etc.
• add tests against the undefined case (which is probably the most common one)