def undocumented(scope = :modified)
      return [] unless scope != :ignore && File.exist?(undocumented_path)
      @undocumented = { modified: [], all: [] } if @undocumented.nil?
      load_undocumented(scope) if @undocumented[scope].empty?
      @undocumented[scope]
    end
def undocumented(scope = :modified)
      return [] unless scope != :ignore && File.exist?(undocumented_path)
      @undocumented = { modified: [], all: [] } if @undocumented.nil?
      load_undocumented(scope) if @undocumented[scope].empty?
      @undocumented[scope]
    end
Returns a list of undocumented symbols in the current diff.

 Available scopes:

  * `modified`
  * `all`

 @param [Key] scope
 @return [Array of symbol]