string_to_date.rb

  # method to evaluate the block for a default value if the
  # conversion to date fails
  # string.to_date return nil if the string is blank
  # so we yield to get the default value from the block there
  # or on a parse error
  def string_to_date(string,&block)
    string.to_date || yield
  rescue => e
    block_given? ? yield : raise
  end