fix(config): ignore empty environment overrides

Author: pollychen-lab

internal/burrito/config/config.go

@@ -242,7 +242,7 @@ func bindEnvironmentVariables(v *viper.Viper, iface interface{}, parts ...string
 			keyParts := append(parts, tv)
 			key := strings.Join(keyParts, ".")
 			envName := "BURRITO_" + strings.ToUpper(strings.Join(keyParts, "_"))
-			if value, exists := os.LookupEnv(envName); exists {
+			if value, exists := os.LookupEnv(envName); exists && value != "" {
 				v.Set(key, value)
 				continue
 			}

internal/burrito/config/config_test.go

@@ -262,3 +262,31 @@ func TestConfig_EnvVarOverridesFlag(t *testing.T) {
 
 	assert.Equal(t, ":8082", cfg.Server.Addr)
 }
+
+func TestConfig_EmptyEnvVarDoesNotOverrideFlag(t *testing.T) {
+	configFile, err := os.ReadFile("testdata/test-config-1.yaml")
+	if err != nil {
+		t.Fatalf("failed to read test configuration file: %v", err)
+	}
+
+	err = os.WriteFile("config.yaml", configFile, 0644)
+	if err != nil {
+		t.Fatalf("failed to create test configuration file: %v", err)
+	}
+	defer os.Remove("config.yaml")
+
+	t.Setenv("BURRITO_SERVER_ADDR", "")
+
+	cfg := &config.Config{}
+	flags := pflag.NewFlagSet("server", pflag.ContinueOnError)
+	flags.StringVar(&cfg.Server.Addr, "addr", ":8080", "server address")
+	if err := flags.Set("addr", ":8081"); err != nil {
+		t.Fatalf("failed to set flag: %v", err)
+	}
+
+	if err := cfg.Load(flags); err != nil {
+		t.Fatalf("failed to load configuration: %v", err)
+	}
+
+	assert.Equal(t, ":8081", cfg.Server.Addr)
+}