toSecret' "return nil, nil" is error-prone

[machine424]

here https://github.com/prometheus/common/blob/098669c08af8eee3da33d1d4a4f242a5242cccb8/config/http_config.go#L781-L797

because the error is nil, we may/would be moving nils around, leading to nil pointer dereference

may be the cause of https://github.com/prometheus/prometheus/issues/16622