class ActiveSupport::HashWithIndifferentAccess

def key?(key)

hash.key?('key') # => true
hash.key?(:key) # => true
hash['key'] = 'value'
hash = ActiveSupport::HashWithIndifferentAccess.new

Checks the hash for a key matching the argument passed in: 
def key?(key)
  super(convert_key(key))
end