code: Reference getInitializingReferenceForConstants() {
      int size = references.size();
      for (int i = 0; i < size; i++) {
        if (isInitializingDeclarationAt(i) || isInitializingAssignmentAt(i)) {
          return references.get(i);
        }
      }
      return null;
    }
docs: Constants are allowed to be defined after their first use.