code: private String convertDefaultValueToString() {
          final Object initialValue = getArgumentValue();
          if (initialValue != null) {
              if (isCollection() && ((Collection<?>) initialValue).isEmpty()) {
                  // treat empty collections the same as uninitialized non-collection types
                  return NULL_ARGUMENT_STRING;
              } else {
                  // this is an initialized primitive type or a non-empty collection
                  return initialValue.toString();
              }
          } else {
              return NULL_ARGUMENT_STRING;
          }
      }
docs: Convert the initial value for this argument to a string representation.