Adds a specific ArgumentError when passing nil to dom_id.

[Austio]

Motivation / Background

I created this PR to make invalid arguments passed to dom_id raise a specific error when it receives an invalid argument.

For example with the following

dom_id(@something_non_existent)

Before this commit it would raise the following: NoMethodError: undefined method 'to_key' for nil:NilClass
After it raises ArumentError: dom_id must be passed a record_or_class as the first parameter, you passed 'nil'

Detail

This PR updates dom_id to validate it's argument and raise an ArgumentError whenever it is passed nil.
The current NoMethodError: undefined method 'to_key' for nil:NilClass error is relatively difficult to identify what is going on because it occurs when the record is cast to a key

The NoMethod error is raised when the argument that is passed to dom_id is sent to record_key_for_dom_id

def dom_id(record_or_class, prefix = nil)
  # nil is passed down the the private method  
  record_id = record_key_for_dom_id(record_or_class) unless record_or_class.is_a?(Class)
   ...
end

# this will raise the error which is harder to identify
def record_key_for_dom_id(record) # :doc:
  key = convert_to_model(record).to_key
  key ? key.join(JOIN) : key
end

Passing a nil argument can happen in many scenarios, but a specific example is misspelling an instance variable

# Set somewhere in your code path
@ivar = 'foo'

# somewhere else, like a view, the @ivar is misspelled
dom_id(@viar)

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: [Fix #issue-number]
• Tests are added or updated if you fix a bug or add a feature.
• CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature. Minor bug fixes and documentation changes should not be included.