presto-base-jdbc/src/main/java/io/prestosql/plugin/jdbc/JdbcIdentity.java/JdbcIdentity/JdbcIdentity
class JdbcIdentity:    public JdbcIdentity(String user, Map<String, String> extraCredentials)
    {
        this.user = requireNonNull(user, "user is null");
        this.extraCredentials = ImmutableMap.copyOf(requireNonNull(extraCredentials, "extraCredentials is null"));
    }