code: public String getValueString() {
          try {
              String s = value.getAsString();
              if (s == null) {
                  throw new RuntimeException("AVA string is null");
              }
              return s;
          } catch (IOException e) {
              // should not occur
              throw new RuntimeException("AVA error: " + e, e);
          }
      }
docs: Get the value of this AVA as a String.
  
  @exception RuntimeException if we could not obtain the string form
  (should not occur)