# Flatten Array

Take a nested list and return a single flattened list with all values except nil/null.

The challenge is to write a function that accepts an arbitrarily-deep nested list-like structure and returns a flattened structure without any nil/null values.
 
For Example

input: [1,[2,3,null,4],[null],5]

output: [1,2,3,4,5]


## Setup

Follow the setup instructions for Crystal here:

http://exercism.io/languages/crystal

More help installing can be found here:

http://crystal-lang.org/docs/installation/index.html

## Making the Test Suit Pass

Execute the tests with:

```bash
$ crystal spec
```

In each test suite all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by changing `pending` to `it`.

## Source

Interview Question [https://reference.wolfram.com/language/ref/Flatten.html](https://reference.wolfram.com/language/ref/Flatten.html)

## Submitting Incomplete Solutions
It's possible to submit an incomplete solution so you can see how others have completed the exercise.