The change introduced in 2be9960 causes values to no longer load from the environment in the presence of SetDefaultsForZeroValuesOnly: true and a non-zero value for the corresponding field.

The following is a quick example to recreate the problem:

type Config struct {
	Username string `env:"USERNAME" envDefault:"admin"`
}
cfg := Config{Username: "root"}
err := env.ParseWithOptions(&cfg, env.Options{
	Environment:                  map[string]string{"USERNAME": "user1"},
	SetDefaultsForZeroValuesOnly: true,
})
if err != nil {
	fmt.Println(err)
	return
}
fmt.Printf("%+v", cfg) // prints `{Username:root}`, but should print `{Username:user1}`

The relevant logic is here:

It does not check to ensure that value was loaded from envDefault rather than from the actual environment.

Thank you for the great library!