Note: I am not using Redux (instead, React Context + reducers)

I have the following reducer:

export default (contents, action) => {
  switch (action.type) {
    case "like-content": {
      let { content } = action;

      const prevContent = contents.get(content.id);

      return new Map([...contents, [content, {
           ...content,
           totalLikes: prevContent.totalLikes + 1 
      }]);
    }

   ...

And I need to check if the given content is stored in my contents map before updating the state.

I have think about updating my code to:

export default (contents, action) => {
  switch (action.type) {
    case "like-content": {
      let { content } = action;

      const prevContent = contents.get(content.id);

      if (!prevContent) throw Error("The content doesn't exist");

      return new Map([...contents, [content, {
           ...content,
           totalLikes: prevContent.totalLikes + 1 
      }]);
    }

 ...

But, personally, it seems incorrect, as I am "breaking" the state update.

How can I handle this?