code: public String get(CharSequence name, String defaultValue) {
          String value = get(name);
          if (value == null) {
              return defaultValue;
          }
          return value;
      }
docs: Returns the value of a header with the specified name.  If there are
  more than one values for the specified name, the first value is returned.
  
  @param name The name of the header to search
  @return The first header value or {@code defaultValue} if there is no such header