diff --git a/tinyviper.go b/tinyviper.go
index 5de5b19..f73a92e 100644
--- a/tinyviper.go
+++ b/tinyviper.go
@@ -27,13 +27,17 @@ type multiResolver struct {
 	resolvers []Resolver
 }
 
-func NewEnvFileResolver(filename string) *EnvFileResolver {
+func NewEnvResolver() Resolver {
+	return EnvResolver{}
+}
+
+func NewEnvFileResolver(filename string) Resolver {
 	readFile, err := os.Open(filename)
 	if err != nil {
-		return nil
+		return EnvFileResolver{make(map[string]string)}
 	}
 	defer readFile.Close()
-	r := &EnvFileResolver{make(map[string]string, 0)}
+	r := EnvFileResolver{make(map[string]string, 0)}
 	fileScanner := bufio.NewScanner(readFile)
 	fileScanner.Split(bufio.ScanLines)
 	for fileScanner.Scan() {
@@ -49,6 +53,9 @@ func NewEnvFileResolver(filename string) *EnvFileResolver {
 
 func (m multiResolver) Get(key string) string {
 	for _, r := range m.resolvers {
+		if r == nil {
+			continue
+		}
 		v := r.Get(key)
 		if r.Get(key) != "" {
 			return v
diff --git a/tinyviper_test.go b/tinyviper_test.go
index 4d99a8d..2829265 100644
--- a/tinyviper_test.go
+++ b/tinyviper_test.go
@@ -2,6 +2,7 @@ package tinyviper
 
 import (
 	"errors"
+	"os"
 	"testing"
 )
 
@@ -10,8 +11,9 @@ type Config struct {
 		Email    string `env:"MY_APP_EMAIL"`
 		Password string `env:"MY_APP_PASSWORD"`
 	}
-	Endpoint string `env:"MY_APP_ENDPOINT"`
-	AppUrl   string `env:"MY_APP_URL"`
+	Endpoint  string `env:"MY_APP_ENDPOINT"`
+	AppUrl    string `env:"MY_APP_URL"`
+	Undefined string `env:"MY_UNDEFINED"`
 }
 
 type testEnvResolver struct{}
@@ -28,7 +30,9 @@ func (t testEnvResolver) Get(key string) string {
 }
 
 func TestConfigErrors(t *testing.T) {
-	cfg := Config{}
+	cfg := Config{
+		Undefined: "foo",
+	}
 	err := LoadFromResolver(&cfg, testEnvResolver{})
 	if err == nil {
 		t.Fatalf("Expected error, got none")
@@ -39,8 +43,10 @@ func TestConfigErrors(t *testing.T) {
 }
 
 func TestConfigNew(t *testing.T) {
-	cfg := Config{}
-	err := LoadFromResolver(&cfg, EnvResolver{}, NewEnvFileResolver(".env.sample"))
+	cfg := Config{
+		Undefined: "foo",
+	}
+	err := LoadFromResolver(&cfg, NewEnvResolver(), NewEnvFileResolver(".env.sample"))
 	if err != nil {
 		t.Error(err)
 	}
@@ -57,3 +63,40 @@ func TestConfigNew(t *testing.T) {
 		t.Error(errors.New("unexpected url"))
 	}
 }
+
+func TestConfigNewWithoutFile(t *testing.T) {
+	cfg := Config{
+		Undefined: "foo",
+	}
+	err := LoadFromResolver(&cfg, EnvResolver{}, NewEnvFileResolver(".env.sample2"))
+	if err == nil {
+		t.Fatalf("Expected error, got none")
+	}
+	if err.Error() != "missing config variables: MY_APP_EMAIL,MY_APP_PASSWORD,MY_APP_ENDPOINT,MY_APP_URL" {
+		t.Error("Expected error, got wrong one: " + err.Error())
+	}
+}
+
+func TestConfigOverride(t *testing.T) {
+	_ = os.Setenv("MY_APP_EMAIL", "someemail2@someprovider.org")
+
+	cfg := Config{
+		Undefined: "foo",
+	}
+	err := LoadFromResolver(&cfg, NewEnvResolver(), NewEnvFileResolver(".env.sample"))
+	if err != nil {
+		t.Error(err)
+	}
+
+	if cfg.UserConfig.Email != "someemail2@someprovider.org" {
+		t.Error(errors.New("unexpected email"))
+	}
+
+	if cfg.Undefined != "foo" {
+		t.Error(errors.New("unexpected app url"))
+	}
+
+	if cfg.UserConfig.Password != "password2" {
+		t.Error(errors.New("unexpected password"))
+	}
+}