def has_key?(key, opts={})
      key = normalize_key(key) if opts.fetch(:normalize, true)
      @source.has_key?(key)
    end
def has_key?(key, opts={})
      key = normalize_key(key) if opts.fetch(:normalize, true)
      @source.has_key?(key)
    end
Lookup whether the key exists.
 @param [String, Symbol] key
 @param [Hash, nil] opts.  :normalize => false will lookup the key as provided.
 @return [Boolean]