postgres create user only if not exists

I have few CREATE user as part of myquery.sql files and it contains few other queries as well

my file looks like this

CREATE USER myuser NOLOGIN;
GRANT CONNECT on DATABSE myDataBase to myuser;
GRANT USAGE ON SCHEAMA myschema to myuser;


I have few queries like this in the same file, due to some reason I need to add new queries to same file, when execute the same file again I stuck with error user already exists, and does not reach to newly added query.

also I checked there is no IF NOT EXISTS kind of help for CREATE USER in postgres.

so how to add the check to create a USER only if not EXISTS.

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