void add(
String name,
Object value
)

Adds a header value. The header named name will have the value value added to its list of values. Some headers are single valued, and for these adding a value will replace the previous value. If the value is of type DateTime a HTTP date format will be applied. If the value is a List each element of the list will be added separately. For all other types the default toString method will be used.

Source

/**
 * Adds a header value. The header named [name] will have the value
 * [value] added to its list of values. Some headers are single
 * valued, and for these adding a value will replace the previous
 * value. If the value is of type DateTime a HTTP date format will be
 * applied. If the value is a [:List:] each element of the list will
 * be added separately. For all other types the default [:toString:]
 * method will be used.
 */
void add(String name, Object value);