Skip insert query if value is null

I have a postgreSQL trigger for my social media project where once a comment is inserted, the trigger inserts a new row into the commentData table and the subscriptions table as shown below.

create or replace function public.initialize_comment_data_subscribe() 
returns trigger as $$
begin
    INSERT INTO "commentData" (comment_id, post_id, vote_count, children_count)
      VALUES (new.id, new.post_id, 0, 0);
    INSERT INTO subscriptions (comment_id, post_id, user_id, email)
      VALUES (new.id, new.post_id, new.author_id, (SELECT email from users WHERE user_id = new.author_id));
    RETURN NEW;
end;
$$ language plpgsql;
create trigger on_create_comment
  after INSERT on comments
  for each row execute procedure public.initialize_comment_data_subscribe();

When the email is null in the users table for a specific user_id, the whole thing fails due to the following line

... (SELECT email from users WHERE user_id = new.author_id));

But instead I would like the first insert to continue working and the second one to be skipped if the email is null.

How do I go about doing this? Or is it better to split the insert queries and have 2 triggers instead.

Do a SELECT INSERT instead:

INSERT INTO subscriptions (comment_id, post_id, user_id, email)
  SELECT new.id, new.post_id, new.author_id, email
  from users WHERE user_id = new.author_id AND email is not null

Skip insert query if value is null

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