postgresql – Why null string values do not work on UPDATE?

I’m using sqlboiler to generated Go models from SQL and I’ve came across the following problem. When specifying ON CONFLICT via sqlboiler code:

dev := models.Device{
    ID:     deviceID,
    Type:   null.StringFrom("device"),
    // Name:        null.StringFrom(""),
    // Alias:       null.StringFrom(""),
}
err = dev.Upsert(context.Background(),
    db,
    true,
    []string{"id"},
    boil.Whitelist("name", "alias", "type"),
    boil.Whitelist("id", "name", "alias", "type"),
)

I get the following query:

INSERT INTO "devices" ("id", "type") VALUES ($1,$2) ON CONFLICT ("id") DO UPDATE SET "type" = EXCLUDED."type","updated" = EXCLUDED."updated"
[60b16bd2890814e5 {device true} ]

and the following error: (X because of minified example)

sql: Scan error on column index X, name \"name\": converting NULL to string is unsupported'

When I initialize Name and Alias with the commented code it all works OK. Why do I need to initialize it? Why can’t zero values work in this scenario?