def parse_address(address, vars)
      return address unless vars.is_a? Hash
      fail(Mailgun::ParameterError, 'Email address not specified') unless address.is_a? String
      if vars['full_name'] != nil && (vars['first'] != nil || vars['last'] != nil)
        fail(Mailgun::ParameterError, 'Must specify at most one of full_name or first/last. Vars passed: #{vars}')
      end

      if vars['full_name']
        full_name = vars['full_name']
      elsif vars['first'] || vars['last']
        full_name = "#{vars['first']} #{vars['last']}".strip
      end 

      return "'#{full_name}' <#{address}>" if defined?(full_name)
      address
    end
def parse_address(address, vars)
      return address unless vars.is_a? Hash
      fail(Mailgun::ParameterError, 'Email address not specified') unless address.is_a? String
      if vars['full_name'] != nil && (vars['first'] != nil || vars['last'] != nil)
        fail(Mailgun::ParameterError, 'Must specify at most one of full_name or first/last. Vars passed: #{vars}')
      end

      if vars['full_name']
        full_name = vars['full_name']
      elsif vars['first'] || vars['last']
        full_name = "#{vars['first']} #{vars['last']}".strip
      end 

      return "'#{full_name}' <#{address}>" if defined?(full_name)
      address
    end
Parses the address and gracefully handles any
 missing parameters. The result should be something like:
 "'First Last' <person@domain.com>"

 @param [String] address The email address to parse.
 @param [Hash] variables A list of recipient variables.
 @return [void]