code: public boolean addCSV(String name, String... values) {
          QuotedCSV existing = null;
          for (HttpField f : this) {
              if (f.getName().equalsIgnoreCase(name)) {
                  if (existing == null)
                      existing = new QuotedCSV(false);
                  existing.addValue(f.getValue());
              }
          }
          String value = addCSV(existing, values);
          if (value != null) {
              add(name, value);
              return true;
          }
          return false;
      }
docs: Add comma separated values, but only if not already present.
  
  @param name   The header to add the value(s) to
  @param values The value(s) to add
  @return True if headers were modified