How to avoid inserting null values in postgres database

Question

I have the following query that inserts data into a many-to-many join table

INSERT INTO playlist_genre(playlist_id, genre_id)
VALUES  (${playlistId}, ${genre1Id}),
        (${playlistId}, ${genre2Id}),
        (${playlistId}, ${genre3Id})
);

However the problem I've come to is that the values genre2Id and genre3Id are not required by the user so could either be an INTEGER or NULL .

I am trying to find a way to write this same query but so it only inserts if a value is present. Both columns have NOT NULL constraints.

Edit :

Here is my Playlist class

class Playlist {
  constructor(playlist) {
    // required fields
    this.title = playlist.title;
    this.playlistType = playlist.playlistType;
    this.userId = playlist.userId;
    this.numberOfTracks = playlist.numberOfTracks;
    this.lengthInSeconds = playlist.lengthInSeconds;
    this.genre1Id = playlist.genre1Id;
    // not required fields
    this.genre2Id = playlist.genre2Id || null;
    this.genre3Id = playlist.genre3Id || null;
    this.description = playlist.description || null;
    this.releaseDate = playlist.releaseDate || null;
  }

  save() {
    return new Promise((resolve, reject) => {
      db.one(sqlCreatePlaylist, this)
        .then((insertedPlaylist) => {
          // Here is where i want to use insertedPlaylist's id 
          // to insert data into 'playlist_genre' table
          resolve(insertedPlaylist);
        })
        .catch(error => reject(error));
    });
  }

Here is what sqlCreatePlaylist looks like

INSERT INTO playlists(
  user_id,
  title,
  playlist_type,
  number_of_tracks,
  duration,
  description,
  release_date
)
VALUES(
  ${userId},
  ${title},
  ${playlistType},
  ${numberOfTracks},
  ${lengthInSeconds},
  ${description},
  ${releaseDate}
)
RETURNING *;

Answer 1

To only insert not nulls:

insert into playlist_genre (playlist_id, genre_id)
select playlist_id, genre_id
from (values
    (${playlistid}, ${genre1id}),
    (${playlistid}, ${genre2id}),
    (${playlistid}, ${genre3id})
) s (playlist_id, genre_id)
where genre_id is not null