code: private void mergeSymbol(Symbol from, Symbol to) {
      for (Node nodeToMove : from.references.keySet()) {
        if (!nodeToMove.equals(from.getDeclarationNode())) {
          to.defineReferenceAt(nodeToMove);
        }
      }
      removeSymbol(from);
    }
docs: Merges 'from' symbol to 'to' symbol by moving all references to point to the 'to' symbol and
  removing 'from' symbol.