Fetch your Environmental Variables

It's important to fetch Ruby environmental variables rather than directly referencing them.

This code depends on 'secret_key':

key = ENV['secret_key']

When 'secret_key' is not set, 'key' will be assigned nil, which is an object.

Later, a call to key.upcase will produce a NoMethodError, because Ruby doesn't know how to uppercase nil.

This is better:

key = ENV.fetch('secret_key')

Now, when 'secret_key' is not set, KeyError will be raised. The code fails fast.

fetch takes a second argument as a default, which means you can even prevent KeyError from ever happening, if you choose:

key = ENV.fetch('secret_key', 'some_default_numbers')

http://ruby-doc.org/core-2.2.3/ENV.html#method-c-fetch